SOUTHERN COD-ICEFISHES: Notothenioidei

PHYSICAL CHARACTERISTICS

Most southern cod-icefishes are about 1 foot (30 centimeters) long, but some species are as short as 4 inches (10 centimeters) or as long as 6 feet (1.8 meters). Most of these fishes have black, brown, or gray mottling on a pale background. They have two or three lateral lines. The lateral (LAT-uhr-uhl) line is a series of pores and tiny tubes along each side of a fish's body and is used for sensing vibrations. Southern cod-icefishes do not have a swim bladder, an internal sac that fishes use to control their position in the water. To help them maintain their position in the water, these fishes have lighter bones than most bottom dwellers and a large amount of oil in their muscles.

GEOGRAPHIC RANGE

All but one species of southern cod-icefishes live just north of Antarctica. One species lives in Antarctica.

HABITAT

Southern cod-icefishes live in streams and estuaries (EHS-chew-air-eez), the areas where rivers meet the sea. Most live on or near the bottom, but some live in open water.

DIET

Some southern cod-icefishes eat anything that comes their way. Others ambush small crustaceans and mollusks. Crustaceans (krus-TAY-shuns) are water-dwelling animals that have jointed legs and a hard shell but no backbone. Mollusks (MAH-lusks) are animals with a soft, unsegmented body that may or may not have a shell.

BEHAVIOR AND REPRODUCTION

Southern cod-icefishes tend to stay on the bottom and rarely swim. Many southern cod-icefishes breed every two years, releasing eggs on or near the bottom. Most larvae hatch six to twelve months after the eggs are released and then live in open water, settling to the bottom after feeding on plankton for six to nine months. Larvae (LAR-vee) are animals in an early stage that must change form before becoming adults. Plankton is microscopic plants and animals drifting in the water.

SOUTHERN COD-ICEFISHES AND PEOPLE

Some southern cod-icefishes have been harvested for fish meal and oil but are most important as food fish.

NATURAL ANTIFREEZE

Many southern cod-icefishes live in seawater that is near its freezing point of about 28.6°F (–1.89°C). They protect themselves by making antifreeze in their bodies.

CONSERVATION STATUS

Southern cod-icefishes are not threatened or endangered.

EMERALD NOTOTHEN (Trematomus bernacchii): SPECIES ACCOUNT

Physical characteristics: Emerald notothen reach a length of about 12 inches (30 centimeters) and a weight of about 12 ounces (350 grams). They are thick-bodied and light brown to pinkish brown on the sides and have dark blotches. The belly is silvery gray. There may be a solid or interrupted white band across the neck and gill cover. These fish are covered with rough scales, except for a patch between the eyes, where there may be a single row of scales.

Geographic range: Emerald notothen live in Antarctica.

Habitat: Emerald notothen live on boulder, rock, or gravel bottoms or in sponge beds. Young fish live in shallow water, and mature fish live in deeper water.

Diet: Emerald notothen eat whatever they can find, mainly bottom-dwelling invertebrates, or animals without backbones.

Behavior and reproduction: Emerald notothen spend most of their time staying still on the bottom. If they swim, it is slowly. These fish live eight to ten years. They can reproduce when they are five years old. Females spawn every two years. The eggs attach to rocks, seaweed, or sponges. Emerald notothen may tend egg masses in sponges.

Emerald notothen and people: Emerald notothen are important in the study of how living things survive in the Antarctic environment.

Conservation status: Emerald notothen are not threatened or endangered. ∎

FOR MORE INFORMATION

Books:

Nelson, Joseph S. Fishes of the World. 3rd ed. New York: Wiley, 1994.

Web sites:

"Emerald Notothen or Emerald Rockcod Trematomus bernacchii." University of California, San Diego. http://scilib.ucsd.edu/sio/nsf/fguide/chordata8.html (accessed on October 28, 2004).