KILLIFISHES AND LIVE-BEARERS: Cyprinodontiformes

PHYSICAL CHARACTERISTICS

Killifishes and live-bearers vary greatly in length from about half an inch (1 centimeter) to nearly 13 inches (33 centimeters). Some of these fishes are sleek, and others are blunt at the ends and flat-topped. Males may be brightly colored, but most females are plain. The fins may have fancy extensions. There is no lateral (LAT-uhr-uhl) line system along the sides, but there is around the head. The lateral line is a series of pores and tiny tubes used for sensing vibrations and usually found along the sides of the body.

GEOGRAPHIC RANGE

Killifishes live all over the world. Live-bearers live in North, Central, and South America.

HABITAT

Killifishes and live-bearers live in heavily planted streams, rivers, lakes, ponds, swamps, desert springs, salt marshes, estuaries (EHS-chew-air-eez) or areas where a river meets the sea, and coastal waters. Some live in temporary bodies of water such as puddles and ditches.

DIET

Killifishes and live-bearers eat fish, plants, invertebrates (in-VER-teh-brehts) or animals without a backbone, animal plankton, waste material, and algae. Plankton are microscopic plants and, in this case, animals drifting in water. Algae (AL-jee) are plantlike growths that live in water and have no true roots, stems, or leaves. Some species of live-bearers eat members of their own species.

BEHAVIOR AND REPRODUCTION

Males of some species of killifishes and live-bearers are aggressively territorial, defending their breeding sites against other males. The fishes that live in temporary habitats such as ditches lay eggs on the bottom and die when the water evaporates. The eggs go into a resting state and hatch in the next rainy season. Killifishes that live in permanent waters spawn, or release eggs, in plants. The eggs stick to the plants. When the young hatch, they are fully capable of swimming and feeding.

KILLIFISHES AND LIVE-BEARERS AND PEOPLE

Some killifishes and live-bearers are eaten. Others are sold as bait. They all help people by eating mosquitos. Aquarium hobbyists keep many species of killifishes and live-bearers. These fishes also are used in medical research.

PRETTY AND PRACTICAL

The beauty of many killifishes and live-bearers has led to their being featured on the postage stamps of several countries, which aids in stimulating an interest in conservation efforts.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists ten species of killifishes and live-bearers as Extinct, five as Extinct in the Wild, eighteen as Critically Endangered, twenty as Endangered, twenty-five as Vulnerable, and three species as Near Threatened. Extinct means no longer in existence. Extinct in the Wild means no longer alive except in captivity or through the aid of humans. Critically Endangered means facing an extremely high risk of extinction in the wild. Endangered means facing a very high risk of extinction in the wild. Vulnerable means facing a high risk of extinction in the wild. Near Threatened means likely to become threatened with extinction in the future. The U.S. Fish and Wildlife Service lists fifteen species as Endangered and one species as Threatened. Endangered means in danger of extinction throughout all or a significant portion of its range. Threatened means likely to become endangered in the near future.

LARGESCALE FOUREYES (Anableps anableps): SPECIES ACCOUNTS

Physical characteristics: Largescale foureyes have large, bulging, froglike eyes set far forward and divided by a black band into upper and lower portions that see above and below the waterline. These fish grow to 12 inches (30 centimeters). They are long and narrow and have a flat head. The dorsal (DOOR-suhl) fin, the one along the midline of the back, is far toward the rear of the body. Three to five blue to purple lines run along the sides of the body. The back is brownish with a whitish line that divides into a Y at the gill cover, each arm ending at an eye.

Geographic range: Largescale foureyes live along the northeast coast of South America.

Habitat: Largescale foureyes live in rivers, streams, and estuaries near beaches.

Diet: Largescale foureyes jump out of the water at low tides to gulp down mud, which is rich in algae, tiny animals, and worms. These fish leap from the water to catch low-flying insects. They also eat small fishes.

Behavior and reproduction: Largescale foureyes see well both above and below the waterline. Because they swim with the upper half of their eyes above the water, they bob their heads up and down to keep their eyes wet. These fish ride breaking waves near sandy beaches, sometimes being tossed onto the beach by the waves. They just jump back into the water. These fish form schools of as many as hundreds of fish.

Largescale foureyes are live-bearers that use internal fertilization (FUR-teh-lih-zay-shun), meaning egg and sperm unite inside the female's body. About twenty weeks after fertilization, ten to twenty young are born. These young fish are as large as 2 inches (5 centimeters) at birth. This size is remarkable because the parents may be only 3½ inches (9 centimeters) long.

Largescale foureyes and people: Largescale foureyes are eaten. To a limited extent, they are sold for aquariums.

Conservation status: Largescale foureyes are not threatened or endangered. ∎

GREEN SWORDTAIL (Xiphophorus hellerii): SPECIES ACCOUNTS

Physical characteristics: Male green swordtails have a long extension on the bottom of the tail fin that forms a sword. Males grow to 51/2 inches (14 centimeters) in total length, the sword being 1½ to 3 inches (4 to 8 centimeters) long. Females grow to 6 inches (16 centimeters). Both sexes have a grayish green background color. Males have two lines of reddish dots on a squared-off dorsal fin and a line of bright to dark red along the entire body. The sword is shiny yellowish green bordered in black.

Geographic range: The native home of green swordtails is Mexico and northwestern Honduras.

Habitat: Green swordtails live in rivers, streams, warm springs and their runoffs, canals, and ponds with heavy plant life.

Diet: Green swordtails eat plants and insects.

Behavior and reproduction: The dominant male in a group of green swordtails drives off rivals in a feeding area or an area where females have grouped. These fish are live-bearers. Males insert their sperm into females. The females can store sperm and produce several broods from a single mating.

Green swordtails and people: Green swordtails are used in the aquarium business and are frequently used in medical research.

Conservation status: Green swordtails are not threatened or endangered. ∎

BLACKFIN PEARL KILLIFISH (Austrolebias nigripinnis): SPECIES ACCOUNTS

Physical characteristics: Blackfin pearl killifish are rarely more than 2 inches (5 centimeters) long. The fins are blue-black with shiny metallic-green borders. There are pearly whitish to greenish spots on all fins and the body.

Geographic range: Blackfin pearl killifish live in Uruguay and Argentina.

Habitat: Blackfin pearl killifish live in temporary waters, such as flooded meadows, shallow ponds, and roadside ditches.

Diet: Blackfin pearl killifish eat insects, worms, and other water-dwelling invertebrates.

Behavior and reproduction: A male blackfin pearl killifish takes over an area that it defends against other males. A female moves in and signals she is ready to reproduce by tilting herself down. The pair spawns on the bottom of the pond or ditch. The eggs laid go into a resting state. When the water evaporates, the adults die, but the eggs survive and then hatch in the next rainy season, within hours of getting wet.

Blackfin pearl killifish and people: Blackfin pearl killifish are exchanged among aquarium hobbyists but are sold only rarely.

Conservation status: Blackfin pearl killifish are not threatened or endangered. ∎

FOR MORE INFORMATION

Books:

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

Gilbert, Carter Rowell, and James D. Williams. National Audubon Society Field Guide to Fishes: North America. New York: Knopf, 2002.

Web sites:

Bayan, Ruby. "Introducing: Livebearers." Freshwater Aquaria. http://oursimplejoys.com/freshwateraquaria/article1005.html (accessed on October 11, 2004).

"Killifish FAQ." American Killifish Association. http://www.aka.org/pages/beginners/faq.html (accessed on October 11, 2004).