Cyprinodontiformes

(Killifishes and live-bearers)

Class Actinopterygii

Order Cyprinodontiformes

Number of families 9

Evolution and systematics

As early as 1828 Wagner recognized a suprageneric category for the group known to us today as the Cyprinodontiformes. In 1835 Agassiz erected the Cyprinodontes as the family containing the genera Cyprinodon, Lebias, Molinesia (correctly spelled Mollienesia), Poecilia, and Anableps. By 1883 the term Cyprinodontidae was in general use for 30 genera and 130 species, as reflected in the work of Jordan and Gilbert. In his classic work The Cyprinodonts, published in 1895, Garman arranged the many genera of the Cyprinodontes into eight subfamilies, and while he erroneously included the characin genus Neolebias and the cyprinid genus Fundulichthys, his systematic view of the constituents of the Cyprinodontiformes is about the same today. This is reflected in the work of Berg, who formally erected the group as the order Cyprinodontiformes in 1940.

In 1964 Rosen placed the Cyprinodontiformes in the superfamily Cyprinodontoidea in the order Atheriniformes. As of 2002 the Cyprinodontiformes were considered a natural group (i.e., a monophyletic group) most closely related to the Beloniformes, the order containing halfbeaks, medakas, needlefishes, sauries, and flyingfishes. Rosen took Garman's eight subfamilies and ordered them into five families, the Cyprinodontidae for all the oviparous genera, the Anablepidae for the viviparous genus Anableps, the Jenynsiidae for the viviparous genus Jenynsia, the Goodeidae for the genera of the viviparous splitfins, and the Poeciliidae for the viviparous genera with gonopodium. In 1924 Hubbs had argued for the placement of Anableps and Jenynsia into the family Anablepidae, a view not adopted by Rosen. The five families of Rosen correspond today to the order Cyprinodontiformes. In Rosen's work there was a clearly defined family-level separation of the lineages into viviparous and oviparous. Essentially, the five families were thought to be related, but there were no proposals about the details of the relationships among the five families or their genera.

It was not until the iconoclastic work of Parenti in 1981 that relationships for the cyprinodontiform genera and their families were proposed. Shared derived characters (evolutionary novelties), not primitive characters, were used to define the various evolutionary lineages in a systematic phylogenetic analysis of the order. Almost all the known genera were reevaluated, and a comprehensive cladogram was constructed to illustrate the proposed interrelationships of the genera and the families into which they were placed. For the first time the order Cyprinodontiformes was defined using only derived characters, consisting of a suite of various osteological features and, in general, a long developmental period and early breeding habits. In the new ordering the viviparous families did not form a monophyletic group, because some live-bearers turned out to be related more closely to oviparous species than to other live-bearers. There were numerous taxonomic and nomenclature changes as the result of the restructuring of the genera as well as the proposed scheme of their relationships.

Three taxonomic arrangements were proposed, wherein viviparous genera were deemed to be sister taxa to oviparous genera. This kind of relationship had not been contemplated previously and constituted a paradigm shift within cyprinodontiform systematics. The viviparous genera Anableps and Jenynsia were recognized as sister taxa because of shared characters in their reproductive biology. These, in turn, were considered the sister group of the oviparous Oxyzygonectes, which had been aligned with Fundulus. These genera constitute the Anablepidae. The viviparous family Goodeidae, with 17 genera, commonly known as splitfins, was realigned with the sister group formed by the oviparous genera Crenichthys and Empetrichthys. This group now constitutes the family Good-eidae, which may be considered to have two subfamilies, the Goodeinae and the Empetrichthyinae. The Poeciliidae, with 27 genera, was placed in a clade with the oviparous African lampeyes, Aplocheilichthys, and its related genera and the

oviparous genus Fluviphylax. That group, in turn, was hypothesized to be the sister group of the Anablepidae.

As a result of these revisions, the killifishes, that is, the oviparous cyprinodontiform genera, are no longer considered to constitute a monophyletic group in the scientific sense, but in the vernacular the term is used commonly. It also should be noted that the Cyprinodontiformes were subdivided into two suborders, the Aplocheiloidei and Cyprinodontoidei, both of which spanned the continents of South America and Africa, with interesting zoogeographical implications.

Four major revisions of the Cyprinodontiformes have been published since 1981. Using both molecular and osteological methods, overall cyprinodontiform taxonomy was revisited, the phylogenetic relationships of the Old World and New World aplocheiloids were revised sharply, and a major restructuring of the Poeciliidae was undertaken. An additional molecular study of the phylogeny of the family Rivulidae and its two subfamilies, the Rivulinae and Cynolebiatinae, was published in 1999, and this may lead to a radical taxonomic and nomenclatural revision of these two subfamilies.

The fossil record does little to illuminate cyprinodontiform origins. The earliest fossils, the cyprinodontid Pachylebias and Prolebias, both found in Europe, date to the Oligocene epoch, 25–40 million years ago (mya). Most fossils date to the Miocene, 10–25 mya. The fossil record is relatively recent compared with the inferred history of the Cyprinodontiformes. The phylogenetic relationships of recent killifishes and live-bearers accord well with the realities of plate tectonics and the breaking up of Gondwana, the single supercontinent formed by present-day South America, Africa, Antarctica, Australia, New Zealand, Madagascar, and India plus an assortment of other small plates not part of the continent of Laurasia, which was positioned to the north of Gondwana.

The distribution of the Cyprinodontiformes on today's widely separated pieces of Gondwana argues for a very ancient origin of this order of fishes, more than three times the age of the oldest-known fossil killifishes. The killifishes and live-bearers originated on Gondwana and were contemporaneous with the dinosaurs. Plate tectonics (continental drift) carried these freshwater fishes to their present locations on a journey that began with the breakup of Gondwana 140 mya. The mountain killifishes, genus Orestias, found in the Altiplano regions of Peru, Bolivia, and Chile, were in place long before the rising of the Andes lifted them to their lofty positions. In general, one can expect some dispersal within zoogeographical areas, but the distribution of freshwater fish families is a result mainly of continental drift.

Before plate tectonic theory, freshwater fish distributions presented great puzzles, the answers to which were sometimes fanciful speculations. For instance, both the African killifish genus Aphyosemion and the South American killifish genus Rivulus were placed in the same subfamily, the Rivulinae. If one thinks of the continents as always being in the same positions, how can the freshwater fishes of these two continents possibly be related, since there is no way small freshwater fishes can swim from Africa to South America? One of the more fanciful hypotheses, ludicrous by today's more sophisticated standards, was that a series of islands spanned the Atlantic Ocean from South America to Africa. The freshwater fishes supposedly swam from island to island, thus accounting for the separation of their families. Then the islands conveniently disappeared without a trace. Another theory held that the continents had moved apart because the earth was expanding. (Two marks on a balloon grow farther apart as the balloon is inflated.) That theory suffers from a lack of any plausible mechanism, although in its early days the theory of continental drift was subjected to the same criticism, a criticism that was answered by the now widely accepted hypotheses of seafloor spreading and subduction.

The systematics of the cyprinodontoid family Poeciliidae parallels the biogeographical situation outlined for the aplocheiloid genera Rivulus and Aphyosemion, since part of the Poeciliidae is South American and part is African. There, too, plate tectonics offers a satisfying explanation of the biogeography of that group.

The taxonomic evaluation of the Cyprinodontiformes is far from complete, and one may reasonably expect many more far-reaching revisions. Many new cyprinodontiform species are being described and will enrich our understanding of this order. In 2000 Lazara pointed out that the number of species described since the first killifish was cited in 1766 by Linnaeus has increased exponentially.

Physical characteristics

The earliest known killifish "description" is a 600-year-old piece of mother-of-pearl jewelry, one inch long, produced by the Native American Mogollon culture in the recognizable shape of Cyprinodon tularosa, endemic to New Mexico. As a general rule, killifishes and live-bearers are sexually dimorphic and dichromatic. In 1881 Steindachner described male and female Cynolebias bellottii as two different species, the female named appropriately Cynolebias maculatus. Cyprinodontiform males and females differ in shape and color and sometimes in numbers of anal and dorsal fin rays, as noted by Steindachner. There is a gestalt to the Cyprinodontiformes that is difficult to describe (because they are so variable) but which makes them instantly recognizable. Few fishes can be mistaken for a killifish or live-bearer, but some of the very few are the mudminnows of the Umbridae. In fact, in 1843 Umbra pygmaea was described by Ayres as a killifish (Fundulus fuscus). Ayres was perhaps the first person to document his confusion about this resemblance.

The Cyprinodontiformes vary greatly in length, from 0.4 in (1 cm), which meets the formal definition of a miniature fish, to nearly 13 in (33 cm). Many are basically cylindrical in shape, with tapering around the caudal peduncle. Some are sleek, pike-like predators and others elongate and flat-topped (the top minnows of the order), with mouths designed for surface feeding. Some are laterally compressed and elongate for fast movement in streams or in pelagic conditions, and others that occupy benthic ecological niches may or may not be compressed but tend to be deep-bodied. Some Orestias have "chunky" body proportions akin to those of various fancy goldfish.

Cyprinodontiformes possess only one dorsal fin, which has its origin anywhere from far forward of the first anal fin ray to a point over the last few anal fin rays. The dorsal fin is never completely ahead and rarely entirely behind the anal fin; there almost always is an overlap. The origin of the anal fin ranges from about the midbody to three-fourths of the way from the snout. Fin rays are soft; Cyprinodontiformes do not have spines. Unpaired fins are rounded, truncated, pointed, elongated, or a combination of these shapes. Caudal fins are sometime lyre-shaped. The unpaired fins may carry very elaborate extensions or filaments, which in some cases extend beyond the caudal fin. Males of most species have contact organs, that is, bony outgrowths along the outer margins of the scales, along the fin rays, or on the snout. These organs help initiate spawning or position the males during spawning. In the live-bearers and some killifishes, the anal fin of the male becomes a gonopodium, which is used as an intromittent organ.

Pelvic fins sometimes are a prominent feature, but mostly they are small, tiny, or absent. Pelvic fin position varies, though usually it is close to the origin of the anal fin; sometimes it is far forward and close to the pectoral fins. There is no lateral line system along the sides, although in some species neuromasts protrude through the scales, running along what normally would be the course of the lateral line. The lateral line system is present around the head, with the cephalic neuromasts either totally exposed or in canals or a combination of the two states. Derived states of the cephalic lateral line system are very useful in taxonomic studies. Some species use the cephalic lateral line system to locate surface prey by its vibrations.

In 1949 Gosline developed an elaborate and very useful classification and numbering system for the sensory canals and pores of the cyprinodontiform head. The anterior naris is tubular in the aplocheiloids and in the cyprinodontoid genera Cubanichthys and Anableps. Among the cyprinodontoids this is considered to be independently derived. Overall squamation is complete, partial, or absent. There has been some attempt, mainly among those studying aplocheiloids, to use the pattern of scales on the head as a taxonomic tool. Upper and lower jaw teeth are spatulate, unicuspid, bicuspid, or tricuspid or have various combinations of those tooth forms. Sometimes teeth

are present on the vomer. Jaw teeth are used to seize food items; teeth on the pharyngeals do the chewing. Mouths are protrusile. In some cases the lower jaw has a marked upward turn, sometimes almost perpendicular to the body axis. Some species have thickened lips to facilitate the eating of algae.

Body proportions and fin lengths and shapes are different in the sexes. Females typically have a more rounded appearance. Aquarists never have problems determining the sex of the Cyprinodontiformes. In other groups, this is not the case. Color differences are always noticeable and, in many cases, dramatic. The females generally are plain—perhaps silvery, olive drab, or brownish—whereas males may be brightly colored in crimson, iridescent greens and blues, bright yellow, bright blue, or a combination constituting a veritable riot of colors.

Distribution

Killifishes have a worldwide distribution, except for Australia, Antarctica, and Europe north of the Pyrenees and the Alps, with the exception of Aphanius fasciatus along the Mediterranean coast of France. Live-bearers are found in North, Central, and South America and the Caribbean.

Habitat

The Cyprinodontiformes occupy such diverse habitats that it is impossible to characterize them in a simple way. A small number of species occur in marine environments, some are brackish water species, and others are even found in hyper-saline waters. Most species, however, inhabit freshwater. Many species, particularly in the genera Aphanius and Cyprinodon, are found in hypothermal environments at temperatures close to their upper lethal limit. Many Rivulus are semiterrestrial and may occur under leaves or logs or move overland from puddle to puddle, pond to pond, and rivulet to rivulet. In some tropical forest areas they are not to be seen until a light rain fills up tire tracks, forms puddles, or fills in the hoof

prints of cows or the footprints of people. Presumably, they are waiting out drier conditions under damp leaf litter until there is enough water in their microhabitats. In small streams they are found along the edges in tiny pockets of water or hidden under the vegetation or stuck on leaves overhanging the water. At least one species, Rivulus marmoratus, inhabits land crab burrows.

Killifishes and live-bearers are found in slow-moving to fast-moving streams, tiny rivulets, shallow sheets of flowing water, puddles, ponds, rivers, lakes, swamps, salt marshes, estuaries, tidal flats, marine coastal waters, isolated desert springs, hypersaline lakes, and springheads. Where the habitats are large, they tend to be at the margins—with some no-table exceptions, such as the pelagic lacustrine species. Almost all of these habitats are heavy with vegetation. Some fishes are found in areas where there are seasonal torrential conditions, which they manage to survive. Perhaps some of the semiterrestrial species leave the water under these conditions. Pelagic forms, while not common, do occur in the high-altitude lakes of the Andes and in some African lakes, most notably, Lake Tanganyika. In both Africa and South America, aplocheiloid killifishes have successfully colonized habitats with seasonal temporary waters. These species lay eggs in the substrate and die off when the water evaporates. The eggs, protected by the substrate, go into a resting state called "diapause." At times the substrate becomes so dry and cracked that it is difficult to imagine that the eggs can survive. When the rains of the wet season fill the shallow pans (in Africa, some are elephant watering holes), roadside ditches, culverts, meadows, temporary swamps, depressions, and ponds that these species inhabit, most but not all eggs hatch within hours, thereby providing a hedge against the false onset of a rainy season. Ironically, in many areas of South America and Africa human intervention in the form of road construction and its associated culverts and ditches has helped these species. Even though some places have two rainy seasons a year, this seasonal characteristic is termed "annualism."

Behavior

Males of the seasonal fishes are aggressively territorial, defending their breeding sites against other males. In aquaria, where retreat is limited, males may fight until one or both die from their injuries. Aggressive territorial behavior is common in the Cyprinodontidae and is known in the Fundulidae (Fundulus catenatus, F. diaphanus, and Lucania goodei). Aggression sometimes extends to nonbreeding females. Male agonistic behavior is very common among the killifishes and some live-bearers and is not necessarily territorial. In the cyprinodontids aggression is associated with the defense of breeding territories; otherwise they move about in peaceful schools. In one cyprinodontid species, Jordanella floridae, the male defends a territory, builds a nest, and fans the eggs—a rare case of cyprinodontiform male parental care. The long-term defense of a breeding territory by most male Cyprinodon likewise confers a degree of protection to the eggs deposited there.

The Poeciliinae, Anablepidae, and Goodeidae are active, gregarious, and sometimes scrappy. When they are not occupied by feeding activities, males posture and display as they seek to mate. Female receptivity behavior is complex. Among the poeciliines, a male sometimes rushes in quickly, thrusting his gonopodium, and then beats a hasty retreat, particularly in those species where the female is much larger. Poeciliine females release a pheromone-like substance, thought to be estrogen, which stimulates males into a mating frenzy. Among the goodeids, members of the genus Allodontichthys behave much like North American darters. In Africa the nonseasonal killifishes inhabit swamps, trickles, very small streams, and occasionally rivers, but usually they occur in vegetation-choked portions at the edges. Here they are distributed singly in small pockets of open water in the weedy margins, under the vegetation itself, or sometimes under the leaf litter on the bottom but never out in the open. Interestingly, one of these species, Aphyosemion franzwerneri, also behaves like a darter. In aquaria, males of all these species range from peaceful to ferociously aggressive toward each other. Those species that exhibit schooling behavior occur exclusively in the suborder Cyprinodontoidei in the families Fundulidae, Cyprinodontidae, Anablepidae, and Poeciliidae. Whether a single species or a mix of species, these schools sometimes are composed of massive numbers of individuals.

Feeding ecology and diet

Cyprinodontiformes are piscivorous, omnivorous, herbivorous, or dedicated to particular food items, such as terrestrial and aquatic invertebrates, zooplankton, detritus, algae, and vascular plants. Some are aggressive feeders and pose a danger to other species when they are introduced outside their natural range. The diet of some species in the Poeciliinae includes a significant cannibalistic component.

Reproductive biology

In the poeciliines, as the male matures, the anal fin is modified into a gonopodium; at the juvenile stage there is no difference between the male and female anal fin. The gonopodium serves as a launching platform for sperm bundles called "spermatozeugmata." In mating the gonopodium is swung forward in a vertical plane and thrust at the female genital opening so as to deposit the sperm bundles either near or inside the opening. The end of the gonopodium has hook-like structures to facilitate the transfer of the spermatozeugmata. It is not known how the bundles are transported to the tip of the gonopodium. Females can store sperm for extended periods of time. Some females are capable of superfetation, that is, they have the ability to carry more than one brood of embryos at different stages of development. There are two gestation extremes: in type 1 the embryo is nourished by the yolk reserves laid down before fertilization ("lecithotrophy"); in type 2 the egg is very small, without much yolk, but the embryo is heavily nourished by maternal fluids transferred by a kind of placenta ("matrotrophy"). There are various inter-grade levels of maternal nourishment, depending on the species. In Tomeurus gracilis, the egg is expelled, and development is external and dependent on the yolk reserve. This exceptional situation is, in reality, an extreme form of type 1 gestation. For the rest of the species with a gestation period, birth is initiated by muscular contractions that rupture the follicular walls of the embryos, thus initiating their exit into the environment.

There are two unisexual poeciliine "species," the all-female Poecilia formosa and Poeciliopsis monacha-lucida. Both so-called species are considered to be of hybrid origin, and some taxonomists do not regard them as true species. Matings are needed to cause these "species" to reproduce. In P. formosa paternal DNA is excluded, and the mating results in an all-female brood. In Poeciliopsis, paternal DNA is not excluded, but the resultant brood is also all female. The origins and relationships of unisexual poeciliines were reviewed by Schultz.

Males of the live-bearing anablepids, the genera Anableps and Jenynsia, have a tubular gonopodium that is used to transfer free spermatozoa, not sperm bundles, to the female. In Anableps dowi sperm bundles are formed but break apart before they make their way down the gonopodium. The gonopodia in these genera swing forward in a horizontal plane but only to one side, the left or the right. The vents of females are accessible only from the left or the right. Thus, left-sided males must mate with right-sided females and vice versa. Embryos are nourished by a pseudo-placenta that transfers nutrients to the enlarged intestine of embryos of Anableps, whereas in Jenynsia the maternal nutrients are supplied through the mouth and opercular opening of developing embryos.

In the viviparous goodeids, the first several anal fin rays of the male are shorter and offset from the rest of the anal fin by a notch. This is the structure by which sperm bundles are transferred, but the exact mechanism of transfer is unknown. Gestating embryos absorb nutritional ovarian fluids by means of elaborate outgrowths, called "trophotaeniae," which form around the anal region of the embryo.

Excluding Rivulus marmoratus, internal fertilization is known in four egg-laying genera, Campellolebias, Cynopoecilus, Epiplatys, and the monotypic Tomeurus. Campellolebias and Cynopoecilus are seasonal genera in the family Rivulidae. Males of Campellolebias have a gonopodium, whereas those of Cynopoecilus have a modified anal fin in which the first six anal fin rays are bunched together and have prominent contact organs along the rays in the form of papillae. Epiplatys is a genus with nearly 50 species, but only one is known to have internal fertilization, a Sudanese population of Epiplatys bifasciatus. Tomeurus gracilis is a typical gonopodial poeceliine species, except that it expels its eggs. The mechanism of sperm transfer in Cynopoecilus and Epiplatys bifasciatus is unknown.

The seasonal fishes lay their eggs in the substrate. Typically, a male defends a territory while mostly hovering over and close to the substrate. A receptive female approaches, angling with her head toward the substrate; the male draws near, sometimes wrapping his anal and dorsal fins around the usually smaller female. The pair dives into the substrate, sometimes disappearing from sight. One or more eggs are released by the female and fertilized by the male. After a characteristic rolling motion designed to bury the eggs, the male and female emerge from the substrate. The eggs enter a resting state. The water in these habitats eventually evaporates, and the adults die or, more likely, are eaten by birds before the water is completely gone. Some of the eggs embryonate and hatch during the next rainy season. Even though the next rainy season may be months or, in a drought, years away, in a home aquarium these eggs may hatch after as little as two to three months of storage in damp peat moss. The spawning of seasonal fish continues through the wet season. The eggs of the seasonal killifishes develop asynchronously in the female, not all at once.

Most nonseasonal killifishes are plant spawners. Males court a passing female and, if she is receptive, the pair move to the vegetation and press their bodies together in a characteristic S shape, their bodies quivering as a single egg is released and fertilized. The eggs are adhesive and stick to the vegetation. Aquarists simulate this habitat by providing a faux plant in the form of a small mop made of acrylic yarn. Aquarists often collect the eggs of these killifishes with their fingers. The egg is tough and easily handled without fear of damage, and it has a long developmental period, 10–14 days. As a result, the young hatch without a yolk sac and are fully capable of swimming and feeding, unlike the young of many other fish groups, which pass through a larval stage.

The species Rivulus marmoratus is a self-fertilizing hermaphrodite, unique among vertebrates in that respect. Individuals of the species look like typical female Rivulus, but they possess both ovaries and testes, with the ability to fertilize their own eggs before laying them. Essentially they are self-cloning. Two types of males are known. Secondary males are hermaphrodites that have become functional males with the color characteristics of a male Rivulus, but they retain a small amount of ovarian tissue. Some populations produce primary males, that is, individuals hatching out as males without ovaries. The populations in the Belize Keys have a high percentage of primary males (25%), and there is some evidence that primary males (and possibly secondary males) mate with the hermaphrodites. This might entail a mechanism whereby the presence of a male prompts suppression of self-fertilization in the hermaphrodites. There are killifishes that spawn in cracks and crevices; typically, these are species found in rocky streams and lakes, the procatopodine genera Procatopus and Lamprichthys tanganicanus, respectively. Some species, such as Fundulus catenatus, lay their eggs over shallow gravel beds. The reproductive biology of many killifishes is not known, even though some of them are fairly common.

Conservation status

Approximately 10% of all cyprinodontiform species—92 in all—are cited in the 2000 Red List of the International Union for Conservation of Nature and Natural Resources (IUCN) in the Extinct (10 species), Extinct in the Wild (5 species), Critically Endangered (18 species), Endangered (20 species), Vulnerable (25 species), Lower Risk/Near Threatened (3 species), and Data Deficient (11 species) categories. The cause of all freshwater fish extinctions and the establishment of the other categories of concern are due solely to the harmful effects of human intervention and not to the events of natural history. Sadly, a species of Cyprinodon described in 1993 was given the species name inmemoriam, since the species was extinct by the time it was described. The Red List is not a static document, and more species may be expected to appear there.

For instance, although huge tracts of the African rain-forests are being cleared, not a single killifish from the affected areas is on the 2000 Red List. This is an extreme example of the category Data Deficient, in this case, no data at all. An undescribed Nothobranchius species from the Caprivi Strip of Namibia is the only African species listed as Endangered. All Nothobranchius habitats, being seasonal, are capable of being severely affected by human activity, so the absence of other Nothobranchius from the 2000 list offers small comfort. Numerous species are listed as Extinct in the Wild. Given the history of failure to keep Extinct in the Wild species, such as the monkey spring pupfish, alive as captive animals, unless they are successfully reintroduced into the wild, the future of such species is bleak.

For species listed in any category the reasons why they were listed are cited. Establishing whether a species is extinct is very difficult because of the nature of extinction. The absence of evidence is not necessarily evidence of absence. The difficulties are acute when the actual distribution of a species is imperfectly known or when its taxonomic limits have not been established or when there has been inadequate sampling. Harrison and Stiassny have reviewed this topic. Another 20 species are listed as regionally endangered by various states in the United States. These statistics need to be put into perspective. The percentage (10%) of the Cyprinodontiformes under threat is among the highest in the Actinopterygii, comparable to the carps, of the order Cypriniformes, with 12% of its 2,660 species appearing on the Red List. Live-bearers and killifishes have colonized marginal habitats easily degraded by human intervention or highly vulnerable to introduced exotic species. In addition, their distributions sometimes are highly localized, as, for example, in a single spring or pond. These factors account for the high level of threat occurring in this group.

Significance to humans

Species in the genera Orestias in the Andes and Anableps in Central and South America are taken in subsistence fishing by local inhabitants. In the bait fish industry in the United States, fundulids, such as Fundulus heteroclitus, and cyprin-odontids,

such as Cyprinodon variegatus, are sold routinely as bait fish. In the case of the latter species this sometimes leads to disastrous consequences for the local fauna when end-ofthe-day bait-bucket releases occur. Both killifishes and live-bearers are voraciously larvivorous, thus helping to control mosquito populations and their resulting detrimental effects upon humans. In many areas killifishes and live-bearers represent an important forage item for game fishes. In the Everglades, Florida Bay, and the Keys there is an interesting food chain of great economic significance. The salt marsh mosquito is very abundant in southern Florida. The killifishes and live-bearers feed heavily on mosquito larvae, obtaining the energy necessary to produce many offspring. When the killifishes and live-bearers move into the tidal creeks, they provide abundant forage for tarpon, redfish, and snook, which feature heavily in the economy of southern Florida.

Aquarium hobbyists keep many species of Cyprinodontiformes. Various live-bearers, selectively bred for color and fancy fins, are sold in large numbers. Many specialty hobbyist groups, such as the American Killifish Association, the Deutsche Killifisch Gemeinschaft, the American Livebearer Association, and the Association France Vivipare, have been formed to keep and study these fishes. The cooperation of hobbyists and ichthyologists has had a significant impact on the furtherance of our knowledge of the Cyprinodontiformes. Cyprinodontiform species have been used widely in evolutionary studies, the study of life history patterns, the study of the effects of exotic introductions, and the disciplines of ecology, reproductive biology, genetics, physiology, toxicology, and behavioral psychology. This list is by no means exhaustive. Xiphophorus hellerii, Fundulus heteroclitus, and Rivulus marmoratus alone have accounted for hundreds of articles in professional journals and other publications. The beauty of many of these fishes has led to their being featured on the postage stamps of several countries, which aids in stimulating an interest in conservation efforts.

Species accounts

List of Species

Largescale foureyes

Anableps anableps

family

Anablepidae

taxonomy

Anableps anableps Linnaeus, 1758, India (misreported type locality).

other common names

English: Striped foureyed fish, foureyed fish, foureye; Spanish: Cuatro ojos; Portuguese: Quatro-olhos.

physical characteristics

Grows to 12 in (30 cm) in total length. Elongate, compressed posteriorly, and flat anteriorly. Blunt snout and toothy horizontal mouth with only a slight curvature. Large, bulging, froglike eyes set far forward, almost on the snout, and divided by a black horizontal band into an upper and lower portion for separately viewing above and below the waterline. Dorsal fin set far back, completely behind the anal fin. Three to five blue to violet horizontal lines of varying lengths run along the sides. Dorsal surface is brownish. A whitish line runs along the back; at the operculum the line divides into a Y shape, each arm of which terminates at an eye. The ventral area is whitish. Sexually dimorphic. Females are larger than males, with rounded fins; males have a tubular, scaled gonopodium.

distribution

Trinidad, Venezuela, Guyana, Suriname, French Guiana, and the Amazon Delta in Brazil.

habitat

Found in freshwater, brackish, and saltwater rivers, streams, and estuaries and oceanic saltwater near beaches.

behavior

A gregarious schooling fish, sometimes gathering in the hundreds with congeners of equal size. Since they swim with the upper half of their eyes above the water, they have the amusing habit of bobbing their heads up and down so as to keep their eyes wet. This species has been seen riding the breakers near sandy beaches, sometimes getting tossed onto the beach by the waves. Undaunted, foureyes just jumps back in. Because of their acute vision above the water, they are very difficult to capture.

feeding ecology and diet

In brackish and marine environments, scores of these fish jump out of the water at low tides to gulp down the mud, which is rich in algae, diatoms, dinoflagellates, amphipods, isopods, and worms. Although they are primarily surface feeders, they leap from the water in pursuit of low-flying insects. Small fishes also are part of their diet, but these fish are not bottom feeders. Not surprisingly, aquarists report that the species will not take food that falls to the bottom of an aquarium.

reproductive biology

Foureyes are live-bearers with internal fertilization and matrotrophic (type 2) gestation and development. The male gonopodium swings out in a horizontal plane, but only in one direction, either to the left or to the right. The vent of the female is covered by a hinged scale called a "foricula," which opens to the left or right. Thus, right-handed males must mate with left-handed females and vice versa, an odd situation that does not seem to impede their reproduction. The gestation period is about 20 weeks, with a brood size of 10 to 20 fry. The young are large, up to 2 in (5 cm) at birth. This large size is remarkable, considering that sexual maturity is reached at about 3.5 in (9 cm).

conservation status

Not listed by the IUCN.

significance to humans

All species are taken for food in subsistence fishing, and, to a limited extent, they are sold in the aquarium trade.

Chocolate lyretail

Aphyosemion australe

family

Aplocheilidae

taxonomy

Aphyosemion australe Rachow, 1921, Port-Gentil (formerly Cape Lopez), Gabon.

other common names

English: Chocolate australe, australe, Cape Lopez lyretail, lyre-tail panchax.

physical characteristics

Grows to 2–2.4 in (5–6 cm). Sexually dimorphic and dichromatic. The male is slender-bodied and cylindrical in shape; the body has a slight curve to the dorsal surface. The head tapers to a terminal mouth, and the caudal peduncle is compressed and tapering. Dorsal fin is small and set far back, with its origin over the midpoint of the anal fin. Dorsal surface is chocolate brown, and anterior flanks are light metallic blue; red spots and splotches are scattered over the body and on the dorsal and anal fins. All fins show color, the dorsal and anal fins with orange and red margins. Anal fin tapers to a point, with its color grading into white; the upper and lower parts of the caudal fin have curved white extensions, giving this fin its characteristic lyre-tailed shape. The female is smaller, usually without much color. Sometimes golden, gray, or muddy, with rounded fins and iridescent bluish white margins on the pectoral fins. Body and unpaired fins have tiny red dots. All color and color patterns vary widely for both males and females.

distribution

South along the coasts of Gabon starting at the Ogowe River, the Congo, the Cabinda Enclave (Angola), and Zaire.

habitat

Found in swamps associated with small streams and rivers, rainforest swamps, and shallow flooded areas—quiet, weed-choked environments.

behavior

A peaceful species, easily kept in a heavily planted aquarium or one provided with spawning mops or with a combination of plants and mops.

feeding ecology and diet

Aquarists feed the chocolate lyretail brine shrimp—frozen or live—adult or newly hatched, and such live foods as fruit flies, daphnia, and tubificid worms. In nature, it is assumed that aquatic invertebrates and terrestrial insects are the chief component of the diet.

reproductive biology

A typical plant spawner, the male courts the female with fins flared. A receptive female moves to the plants or spawning mop, where the pair presses against each other in an S shape, both of them quivering. The female releases an egg, which the male fertilizes. The adhesive egg sticks to the vegetation or mop. These eggs are collected easily and hatch in 14 days. It is estimated that some aquarium populations of the chocolate lyretail have been held and bred in aquaria continuously since 1913, yet differences are small compared with the wild forms from the type locality.

conservation status

Not listed by the IUCN.

significance to humans

Sold and exchanged among aquarium hobbyists and occasionally available in the aquarium trade.

Devils Hole pupfish

Cyprinodon diabolis

family

Cyprinodontidae

taxonomy

Cyprinodon diabolis Wales, 1930, Devils Hole, Ash Meadows, Nevada, United States.

other common names

None known.

physical characteristics

A dwarf species seldom exceeding 1 in (2.6 cm) in length. Pelvic fins are absent. Resembles the juvenile pupfish. Sexually dimorphic and dichromatic. Males have iridescent blue body color; the operculum is iridescent with a purple sheen. The unpaired fins are bordered in black, the dorsal fin is iridescent gold, and the anal and caudal fins are whitish toward the base. Prominent genital papilla. Females overall have more yellowish coloration than males. The back and caudal and pectoral fins are yellowish brown, and the dorsal fin is edged in black. The operculum is metallic green, with a hint of a dark bar on the caudal peduncle.

distribution

Ash Meadows, Nevada.

habitat

The enclosed pool of an aquifer formed by flooded limestone caverns and reached by a 49 ft (15 m) naturally occurring shaft in the side of a hill, its only source of light. The dimensions of the entire pool are 11.5 ft by 72 ft (3.5 m by 22 m). A boulder divides the surface of the pool into two sections. The breeding and most of the feeding, upon which the survival of the species depends, take place on an algae-covered rocky shelf 11.5 ft by 16.6 ft (3.5 m by 5 m) with 1 ft (0.3 m) of water above it. The shelf is situated at the foot of the shaft. The overall dimensions of this part of the pool are 11.5 ft by 42 ft (3.5 m by 13 m). At the end of the shelf there is an abrupt drop-off of 28 ft (8.5 m). The substrate continues to slope downward below that depth. Water flows in and out of the pool at a year-round temperature of 90°F (32°C). As the lakes and waters of the area disappeared and the desert formed, the species was trapped in the aquifer 10,000 to 25,000 years ago.

behavior

The pupfish exhibits a daily cycle of movement to and from the rocky shelf, depending on the time of day and the time of year.

feeding ecology and diet

In the summer and fall the species feeds chiefly on the algae growing on the shelf. Algae also grow on the substrate just off the shelf up to a depth of 50 ft (15 m), with only trace amounts below that. In winter and spring, when the algae are much reduced, diatoms are the chief food items. The population varies from about 200 to 500 individuals, depending on the algae growth.

reproductive biology

Males do not set up breeding territories, as do other pupfish. Spawning takes place primarily in April and May. Males closely accompany a ripe female to the algae-covered shelf, where they stay together and spawn at irregular time intervals spanning about one hour. The species has spawned in the laboratory, but no eggs were hatched.

conservation status

Listed as Vulnerable by the IUCN.

significance to humans

The pupfish has endured in its tiny habitat for as many as 25,000 years, providing us with a stimulus to ponder both the durability and the vicarious nature of life.

Ascotan Mountain killifish

Orestias ascotanensis

family

Cyprinodontidae

taxonomy

Orestias ascotanensis Parenti, 1984, Salar de Ascotan, Chile.

other common names

English: Lake Ascotan Mountain killifish

physical characteristics

Grows to 2.4 in (6 cm) in length. A member of the Orestias agassizii species complex. Basically olive-green in color, with anal and dorsal fins set back and over each other. The lower jaw turns up. Males and females are robust, with a relatively large head compared with the heads of other species in the species complex. Sexually dimorphic and dichromatic. Males are smaller than females and more slender. Breeding males have a bright yellow overlay on the sides and the anal and dorsal fins. Females are larger and more rounded than males. The fins and body are mottled, tending toward more uniform coloration when they are very mature.

distribution

Known only from Salar de Ascotan, a small saline lake in northwestern Chile, the southernmost population of Orestias.

habitat

The species is found in the slightly brackish water of Lake Ascotan and its associated ponds, where Ruppia filifolia is the most common vegetation.

behavior

In 1995, for the purpose of studying captive breeding, Jara, Soto, and Palma set up four males and four females in a planted 3 gallon (12 L) aquarium with no reported aggression among the males. The males did not persistently court the females, as happens with many other killifishes; some time was spent apart, feeding and moving about the aquarium.

feeding ecology and diet

In aquaria the species readily feeds on insect larva, crustaceans, and commercial flake food, indicating that in the wild it is a benthopelagic feeder on aquatic invertebrates.

reproductive biology

This species is a typical plant spawner. At the lake, eggs were found attached to the vegetation. In aquaria the male courts the female by approaching from beneath and nudging her pelvic area. The two then move to the vegetation. With the pair positioned side by side with their vents close together, the male assumes a typical S-shape posture. The female releases two or three adhesive eggs, which are fertilized by the male. The filamentous eggs adhere to the vegetation. The incubation time is about 17 days at 63–68°F (17–20°C).

conservation status

Not listed by the IUCN.

significance to humans

None known.

Northern mummichog

Fundulus heteroclitus macrolepidotus

family

Fundulidae

taxonomy

Fundulus heteroclitus macrolepidotus Walbaum, 1792, northern America. In the 1980s, Able and Felley recognized the sub-species status of the northern populations of Fundulus heteroclitus.

other common names

English: Killie, killifish; Spanish: Fúndulo; Portuguese: Fundulo.

physical characteristics

Grows to 5 in (13 cm) in length. Sexually dimorphic and dichromatic. Males and females have up to 15 vertical bars, which tend to be faint or missing in mature adults. The mouth is blunt, with a turned-up lower jaw. The dorsal fin is positioned over the anal fin origin at about the midbody. Males have a dorsal ocellus. Breeding males are light gray to very black in background color. The body and all unpaired fins have bright iridescent white to greenish opalescent spots. The dorsal, anal, and caudal fins have a yellow margin that is less noticeable on the caudal fin in the black body variety. There is a yellowish cast to the abdomen and operculum, the latter with iridescent silver highlights. Color patterns and color intensities vary widely in both sexes. Females are larger than males. Body is chunky with a pale silvery background, brownish color on the back, and whitish color on the abdomen. The fins are clear. Adults rarely are confused with other species in their natural range.

distribution

From Chesapeake Bay, Maryland, United States, to Newfoundland, Canada. Naturalized in the estuary of the Guadalquivir River, southwestern Spain, and possibly established in the salt marshes of the estuary of the Guadiana River, at Castro Marim, southeastern Portugal.

habitat

The species is active primarily in tidally influenced coastal salt marshes as well as estuaries, tidal streams and creeks, shallow marine and brackish environments, and back-beach lagoons reached by high tides. They have been reported for freshwater portions of the Bronx River and naturalized in freshwater impoundments, the latter likely due to bait-bucket releases. Most studies of its habitat use have been undertaken in its primary habitat, the salt marshes.

behavior

Traveling in huge schools numbering in the hundreds, the mummichog is in constant search of food. As a result, fishers find that they are caught easily in baited minnow traps. As a predator on salt marsh invertebrates and small fish, and as a prey item for wading birds and the blue crab, the northern mummichog has a significant impact on salt marsh trophic dynamics. The annual mortality rate is about 50% for adults and more than 99% for the larval and juvenile class sizes.

feeding ecology and diet

Feeds on a variety of marine and freshwater invertebrates, diatoms, mollusks, amphipods, crustaceans, plant material, insects, detritus, worms, and small fishes. It is doubtful that a mummichog would spurn anything edible that fits into its mouth. Mummichogs are preyed upon by larger fish and fish-eating birds.

reproductive biology

Judging by its reproductive behavior in aquaria, the mummichog probably spawns continually in the spring and summer, but in nature its peak spawning activity is governed by a lunar cycle. Eggs are laid in clumps on floating algae mats or at the base of marsh grasses and buried in the sand in the high marshes at the very high tides of the new moon or full moon. The eggs are placed where desiccation will be minimized when the tide goes out. The eggs hatch when they are immersed again at the next very high tide. In aquaria water-incubated eggs hatch in about 16 days.

conservation status

Not listed by the IUCN.

significance to humans

The mummichog is used as a bait fish and as an aquarium animal; it also is one of the most widely used laboratory animals. It is a harmless species unless it is swallowed live. It has been reported that many bored fishers have swallowed live mummichogs. In one such instance, some of the fish were infected with the larva of the nematode Eustrongyloides ignotus, causing stomach and intestinal problems for three fishers, two of whom required surgical intervention. Raasch noted, "Though 12 fishermen reported no symptoms from this pastime, the moral is that fishermen should abstain from taking the bait themselves when the fish refuse to do so."

Redtail splitfin

Xenotoca eiseni

family

Goodeidae

taxonomy

Xenotoca eiseni Rutter, 1896, near Tepic, Nayarit, Mexico.

other common names

Spanish: Mexcalpique cola roja.

physical characteristics

Males grow to 2.4 in (6 cm) in length and females to 2.8–3 in (7–8 cm). Sexually dimorphic and dichromatic. All fins are rounded. The dorsal fin of males is larger than that of females and is set over the anal fin, far back on the portion of the body that tapers to the caudal peduncle. The body is block-shaped, with a humpbacked appearance in mature fish. The depth of the caudle peduncle is much smaller than the body depth. The head is small and pointed. The basic background color of the body is brownish gray to beige; the degree of dark pigmentation is quite variable. Males are bright orange to red at the base of the caudal peduncle, with iridescent blue highlights on the forward part of peduncle between the anal and dorsal fins. The middle portion of the body has gold highlights, and the abdomen is reddish to yellowish near the operculum. The dorsal fin is sometimes black, the caudal fin is orange to yellow, and the anal fin is orange. Color patterns and intensities vary greatly by location, with colors in alpha males very pronounced. Females have a grayish beige body color, sometimes with silvery highlights; all fins are slightly yellow.

distribution

Mexico in Rio San Leonel, El Sacristan, and Rio Grande de Santiago drainages in Nayarit; also in Rio Tamazula, Jalisco.

habitat

Found in rivers, streams, and springs as well as in ditches, which are sometimes highly polluted.

behavior

Collects in groups that have an alpha male. Males constantly pursue females and are pugnacious and scrappy toward each other and especially toward other species. In aquaria they have the reputation of being fin nippers.

feeding ecology and diet

Omnivorous.

reproductive biology

A live-bearing species with internal fertilization, the embryos being nourished by trophotaeniae. The gestation period is about 60 days. Brood size ranges from 10 to 40 fry, with reports of up to 100 fry.

conservation status

Not listed by the IUCN.

significance to humans

The redtail splitfin is sold in the aquarium trade and is bred and traded by live-bearer aquarium hobbyists.

Tanganyika pearl lampeye

Lamprichthys tanganicanus

family

Poeciliidae

taxonomy

Lamprichthys tanganicanus Boulenger, 1898, Mbiti Rocks, southernmost Lake Tanganyika.

other common names

English: Lake Tanganyika lampeye, Tanganyika pearl killifish, Tanganyika killifish.

physical characteristics

Grows to 6 in (15 cm) in length. Sexually dimorphic and dichromatic. Males and females are silvery, sleek, and compressed and taper to the terminal mouth and caudal peduncle. Brightly reflective eyes. They have high-set pectoral fins and dorsal fins set far back, with the origin approximately over the middle of the anal fin. Caudal fins have scales at the base. Recurved teeth noticeable on the outer surface of the upper and lower jaws. Males have an anal fin with a broad base; the rays are shorter than in females. Eight or nine lines of very bright iridescent blue spots along the body, with yellowish spotting on dorsal, anal, and caudal fins and yellow pelvic fins. All observed colors and patterns vary widely, depending on the angle of the lighting. Female are smaller than males, with rounded fins. Shorter dorsal and anal fin base, anal fin rays longer than in the male. The body is silvery or bluish, and the fins are faintly yellow or orange.

distribution

Endemic to Lake Tanganyika.

habitat

Rocky shores (not sandy areas) out to a depth of about 30 ft (10 m).

behavior

A benthopelagic fish moving in large schools with conspecifics and sometimes in schools of native freshwater herrings. Despite its predilection for schooling, individuals wander about apart from schools. Males are not aggressive toward each other. Fry form huge schools in the hundreds and even in the thousands. In aquaria newly hatched fry form schools at the water surface immediately upon hatching. Fry must be reared apart from the adults.

feeding ecology and diet

Feeds on aquatic and terrestrial insects, such as chironomid larvae, termites, and beetles, as well as small crustaceans, ostracods, fish scales, and small fish. The elements of this diet indicate feeding from the bottom to the surface of the water column. The recurved teeth on the outer surface of the upper and lower jaws facilitate the capture of chironomid larvae and ostracods on rocky substrates. Fish scales and small fishes indicate midwater feeding, while terrestrial insects suggest surface feeding. Aquatic vegetation does not seem to play a part in the diet.

reproductive biology

A bottom spawner, utilizing cracks and crevasses for its egg-deposition sites. A male and female meeting in midwater descend to the rocky substrate. The female positions herself close to a crack or crevasse in the rocks, where she ejects an egg, which is fertilized by the male. The eggs are not adhesive but become wedged in place. In aquaria they make use of a similar arrangement of rocky crevasses but also lay their eggs in spawning mops and even on the bare bottom of the aquarium. The eggs are large, 0.1 in (3 mm), but difficult to see. Eggs eye-up in about a week and hatch in two to three weeks.

conservation status

Not listed by the IUCN.

significance to humans

Occasionally appears in the aquarium trade.

Green swordtail

Xiphophorus hellerii

family

Poeciliidae

taxonomy

Xiphophorus hellerii Heckel, 1848, Orizaba, Mexico.

other common names

English: Swordtail; Spanish: Cola de espada.

physical characteristics

Males grow to 5.5 in (14 cm) in total length, with a sword length of 1.6–3 in (4–8 cm). Females grow to 6.3 in (16 cm). Sexually dimorphic. Males and females have basically the same grayish green background color. Males have a gonopodium, a slender body, a long extension on the bottom of the caudal fin forming a "sword," two lines of reddish dots on a squared-off dorsal fin, and a pronounced line of color that is bright to dark red to almost brown running longitudinally along the body from the snout through the eye to the base of the caudal fin. Sometimes paralleled on the flanks by one or two fainter reddish lines above and below. The sword is an iridescent yellowish green bordered in black. Females are robust and rounded, with squared-off anal and dorsal fins. Caudal fin is asymmetrically rounded, with a hint of a protrusion from the lower part of the fin. There is a shadow on the area over the vent (gravid spot).

distribution

Native distribution in Rio Nantla, Veracruz, Mexico, to northwestern Honduras. Naturalized in the continental United States (ten states) and Hawaii; Michoacan, Morelos, Nuevo Leon, and Coahuila, Mexico; Transvaal, South Africa; Sri Lanka; New Caledonia, Australia; Fiji; Guam; Réunion; and Madagascar.

habitat

Inhabit rivers, streams, warm springs and their runoffs, canals, and ponds with heavy vegetation.

behavior

While they are not territorial, male swordtails form hierarchical groups. A dominant male drives off rivals within a feeding domain or an area where females have congregated. The mating success rate of a dominant male is about 80% within his area of activity. Females form hierarchical groups of several individuals that stay in close proximity to a dominant male.

feeding ecology and diet

Plant material and insects form the greatest part of the diet. In aquaria they are voracious, consuming a wide variety of foods, such as fruit flies, frozen or live brine shrimp and chironomid larvae, flake foods, high-protein paste foods, small fish, and algae.

reproductive biology

Green swordtails are live-bearers. Males impregnate females by means of a gonopodium. Females can store sperm and may produce, from a single mating, several broods over an eight-month period. Swordtails undergo lecithotrophic (type 1) gestation and development, with fry being produced approximately every 30 days. Brood sizes are fairly large; 100 or more fry may be produced by a large female.

conservation status

Not listed by the IUCN.

significance to humans

The green swordtail has considerable economic importance in the aquarium trade and frequently is used in genetic and behavioral research.

Blackfin pearl killifish

Austrolebias nigripinnis

family

Rivulidae

taxonomy

Austrolebias nigripinnis Regan, 1912, La Plata, Argentina.

other common names

Vernacular: Nigripinnis.

physical characteristics

A small species, 2–2.75 in (5–7 cm) and rarely more than 2 in (5 cm) long. Relatively deep-bodied and sexually dimorphic and dichromatic. Males are larger than females. All fins are blue-black with an iridescent greenish overlay on the pectorals. Fins are rounded, with relatively large anal and dorsal fin bases. Iridescent metallic-green margin on the dorsal fin and similar margins on the anal and caudal fins are made up of a series of separate spots. Opalescent whitish to greenish spots on all fins and the body, forming five to 11 vertical bars. Lines paralleling the fin edges on the unpaired fins. Body color is sometimes pale around the abdomen. All intensities and patterns vary widely. The female has smaller rounded fins and brown mottling on the body, dorsal fin, and anal fin. Clear caudal, ventral, and pectoral fins and whitish abdominal area.

distribution

The La Plata River basin in Uruguay and Argentina.

habitat

Inhabit temporary waters, such as flooded meadows, shallow ponds, and roadside ditches.

behavior

The male takes over an area, which it defends against other males. A female moves in, signaling her receptivity by tilting toward the substrate. The male joins the female, and they move side by side with their heads together. The pair spawns directly on the substrate or, conditions permitting, by diving into it. In an aquarium with more than one male, a dominant male, obvious by his black body and fins, defends a spawning area of his choice; the color of the other males fades to light gray, with some black or brownish blotching. If the aquarium is heavily planted so that the males cannot see each other, more than one dominant male may appear.

feeding ecology and diet

The species feeds on live foods, such as aquatic and terrestrial insects, worms, crustaceans, and other aquatic invertebrates. In aquaria live foods (such as fruit flies, brine shrimp, chironomid larvae, tubificid worms, and daphnia) are accepted eagerly and almost everything else is rejected, with the exception of chopped earthworms and certain paste foods.

reproductive biology

Eggs placed in the substrate during spawning go into diapause. When the temporary waters evaporate, the adults die off, but the eggs survive until they hatch in the next rainy season, within hours of being wetted. Aquarists simulate this environment by providing garden peat moss as the substrate, periodically collecting the peat and storing it away in an almost dry state at a temperature of about 70°F (20°C). When the peat is flooded after two to four months of storage, most of the eggs will hatch. If the eggs do not hatch, the peat can be dried again and flooded at a later date.

conservation status

Not listed by the IUCN.

significance to humans

The blackfin pearl killifish is exchanged among aquarium hobbyists but only rarely becomes available in the aquarium trade.

Mangrove rivulus

Rivulus marmoratus

family

Rivulidae

taxonomy

Rivulus marmoratus Poey, 1880, "from Cuba, if they do not exist in the United States." Poey's description of the type locality has to be one of the strangest in the history of taxonomy. As it turns out, this species is found in Florida and Cuba; the types are presumed to be from Cuba, Poey's homeland.

other common names

English: Rivulus.

physical characteristics

Grows to 3 in (75 mm) in length. Hermaphrodites. Cylindrical in shape, with tapering of the head and caudal peduncle and a high scale count. Dorsal and anal fins are set far back (typical for all Rivulus species), with the dorsal fin origin set back farther than the anal fin origin. A characteristic splotchy brown pattern, with an irregular dark mark just behind the operculum (humeral blotch) and a rivulus spot (ocellus) on the caudal peduncle. Primary and secondary males have the same body shape, an orange or pink overlay (more often orange) on the body and fins, mottling, and a dark humeral blotch. The rivulus spot sometimes is absent, unpaired fins at times are clear and at times have dark edges. The proportion of primary males in Belize is high (25%), whereas elsewhere the proportion is very low for both primary and secondary males.

distribution

Florida, Mexico, Belize, Nicaragua, Guatemala, Honduras, French Guiana, Venezuela, Brazil as far south as Santos, the Bahamas, and numerous Caribbean locations.

habitat

A semiterrestrial species that inhabits coastal mangrove forests in very shallow water or the wet areas of their muddy flats, out of water under detritus and leaf litter, or under or inside rotting logs. Frequently occurs in the burrows of land crabs. Found in marine and brackish water or in hypersaline pools but not in freshwater.

behavior

Can be caught in traps set in crab holes but dies if the traps become flooded, possibly indicating that respiration of atmospheric air is a necessity. They also can be caught on a tiny hook baited with a small piece of worm. Captive individuals jump out of the water to snatch a termite or ant held above the water surface. In nature they flip along the water surface one or more times or leave the water altogether to elude danger. Extremely aggressive toward each other in aquaria, yet small aggregations have been caught in crab burrows and under rotting logs.

feeding ecology and diet

Feeds on small terrestrial and aquatic insects, mosquito larvae, polychaete worms, mollusks, and gastropods. It leaves the water to seize food items but returns to the water to eat them.

reproductive biology

The only known self-fertilizing vertebrate. Although they are highly efficient at self-fertilization, hermaphrodites release some unfertilized eggs. There is evidence that outcrossing takes place, which would seem to indicate that the hermaphrodites can suppress self-fertilization so that males can fertilize the unfertilized eggs released by the hermaphrodites.

conservation status

Not listed by the IUCN. Regionally are listed as a species of Special Concern in Florida.

significance to humans

Widely used in field and laboratory studies in genetics, toxicology, ecology, and physiology.

Resources

Books

Berra, Tim M. Freshwater Fish Distribution. San Diego: Academic Press, 2001.

Brichard, Pierre. Pierre Brichard's Book of Cichlids and All Other Fishes of Lake Tanganyika. Neptune City, NJ: T.F.H. Publications, 1989.

Costa, Wilson J. E. M. Pearl Killifishes. The Cynolebiatinae: Systematics and Biogeography of the Neotropical Annual Fish Subfamily (Cyprinodontiformes: Rivulidae). Neptune City, NJ:T.F.H. Publications, 1995.

——. "Phylogeny and Classification of the Cyprinodontiformes (Euteleostei: Atherinomorpha): A Reappraisal." In Phylogeny and Classification of Neotropical Fishes, edited by L. R. Malabarba, R. E. Reis, R. P. Vari, Z.M. Lucena, and C. A. S. Lucena. Porto Alegre, Brazil: EDIPUCRS, 1998.

Etnier, David A., and Wayne C. Starnes. The Fishes of Tennessee. Knoxville: University of Tennessee Press, 1993.

Frickhinger, Karl Albert. Fossil Atlas: Fishes. Blacksburg, VA: Tetra Press, 1996.

Harrison, Ian J., and Melanie L. J. Stiassny. "The Quiet Crisis: A Preliminary Listing of the Freshwater Fishes of the World That Are Extinct or 'Missing in Action.'" In Extinctions in Near Time: Causes, Contexts, and Consequences, edited by Ross MacPhee. New York: Kluwer Academic/Plenum Publishers, 1999.

Hilton-Taylor, C., comp. 2000 IUCN Red List of Threatened Species. Gland, Switzerland, and Cambridge, U.K.: IUCN, 2000.

La Rivers, Ira. Fish and Fisheries of Nevada. Reno: University of Nevada Press, 1994.

Lazara, Kenneth J. The Killifish Master Index: The Killifishes, an Annotated Checklist of the Oviparous Cyprinodontiform Fishes. 4th edition. Cincinnati: American Killifish Association, 2000.

Mayden, Richard L., ed. Systematics, Historical Ecology, and North American Freshwater Fishes. Stanford: Stanford University Press, 1992.

Meffe, Gary K., and Franklin F. Snelson, Jr., eds. Ecology and Evolution of Livebearing Fishes (Poeciliidae). Englewood Cliffs: Prentice Hall, 1989.

Minckley W. L., and James E. Deacon, eds. Battle Against Extinction, Native Fish Management in the American West. Tucson: University of Arizona Press, 1991.

Page, Lawrence M., and Brooks M. Burr. A Field Guide to Freshwater Fishes of North America North of Mexico. Boston: Houghton Mifflin, 1997.

Raasch, Maynard S. Delaware's Freshwater and Brackish-Water Fishes: A Popular Account. Neptune City, NJ: T.F.H. Publications, 1996.

Schultz, R. Jack. "Origins and Relationships of Unisexual Poeciliids." In Ecology and Evolution of Livebearing Fishes (Poeciliidae), edited by Gary K. Meffe and Franklin F. Snelson, Jr. Englewood Cliffs: Prentice Hall, 1989.

Seegers, Lothar. Killifishes of the World: Old World Killis I— Aphyosemion, Lampeyes, Ricefishes. Mörfelden-Walldorf: Verlag A.C.S., 1997.

——. Killifishes of the World: Old World Killis II—Aplocheilus, Epiplatys, Nothobranchius. Mörfelden-Walldorf: Verlag A.C.S., 1997.

——. Killifishes of the World: New World Killis—Cyprinodon, Cynolebias, Rivulus. Mörfelden-Walldorf: Verlag A.C.S.,2000.

Smith, C. Lavett. The Inland Fishes of New York State. Albany: New York State Department of Environmental Conservation, 1985.

Wildekamp, Rudolf H. A World of Killies: Atlas of the Oviparous Cyprinodontiform Fishes of the World. Mishawaka, IN: American Killifish Association, 1993.

Wischnath, Lothar. Atlas of Livebearers of the World. Neptune City, NJ: T.F.H. Publications, 1993.

Periodicals

Able, Kenneth W., and James D. Felley. "Geographical Variation in Fundulus heteroclitus: Tests for Concordance Between Egg and Adult Morphologies." American Zoologist 26, no. 1 (1986): 145–157.

Baugh, Thomas. M., and James E. Deacon. "Daily and Yearly Movement of the Devil's Hole Pupfish Cyprinodon diabolis Wales in Devil's Hole, Nevada." Great Basin Naturalist 43, no. 4 (1983): 592–596.

——. "Maintaining the Devil's Hole Pupfish Cyprinodon diabolis Wales in Aquaria." Journal of Aquariculture and Aquatic Sciences 3, no. 4 (1983): 73–75.

——. "The Most Endangered Pupfish." Freshwater and Marine Aquarium 6, no. 6 (1983): 22–26, 78–79.

Beaugrand, Jacques P., Jean Caron, and Louise Comeau. "Social Organization of Small Heterosexual Groups of Green Swordtails (Xiphophorus hellerii, Pisces, Poeciliidae) Under Conditions of Captivity." Behaviour 91 (1984): 24–60.

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Organizations

American Killifish Association. 280 Cold Springs Drive, Manchester, PA 17345-1243 USA. Web site: <http://www.aka.org>

American Livebearer Association. 5 Zerbe Street, Cressona, PA 17929-1513 USA. Phone: (570) 385-0573. Fax: (570) 385-2781. Web site: <http://livebearers.org>

Desert Fishes Council. 315 East Medlock Drive, Phoenix, AZ 85012 USA. Phone: (602) 274-5544. Web site: <http://www.desertfishes.org/>

Kenneth J. Lazara, PhD