SOUTH AMERICAN KNIFEFISHES AND ELECTRIC EELS: Gymnotiformes

PHYSICAL CHARACTERISTICS

South American knifefishes and electric eels have a narrow ribbon-like body. Instead of a tail fin, they have a long tail. The tail is an extension of the anal (AY-nuhl) fin, the fin on the midline of the belly, which on these fishes extends the entire length of the belly. There are no pelvic fins, the rear pair, or dorsal (DOOR-suhl) fin, the fin along the midline of the back. The most outstanding feature of knifefishes and electric eels is electric organs in the skin. Electric eels give off strong electric discharges. Knifefishes produce weak electrical discharges.

GEOGRAPHIC RANGE

South American knifefishes and electric eels live in South America and Central America.

HABITAT

South American knifefishes and electric eels live in small streams, large rivers, lakes, and various types of backwaters. Many of these fishes live in deep, main-river channels. Some live in water with low oxygen content and gulp air at the water surface. Most of these fishes tolerate very warm water.

DIET

Some South American knifefishes and electric eels eat mostly young insect larvae (LAR-vee), worms, and crustaceans (krus-TAY-shuns), water-dwelling animals that have jointed legs and a hard shell but no backbone. Some have large mouths and feed on large prey. Some feed on scales. Some have a long, curved mouth and search for insect larvae in holes and crevices.

BEHAVIOR AND REPRODUCTION

South American knifefishes and electric eels can regrow the hind parts of their bodies. They are active at night and hide during the day among plants, in floating meadows, in crevices and holes, and under various kinds of shelter. During the day some species lie flat and motionless on the bottom, imitating leaves. Some species burrow in the sand during the day.

South American knifefishes and electric eels spawn, or release eggs, every few days to every few weeks. Knifefishes reproduce during the high-water season, and eels during the dry season. During courtship, the electrical discharges serve various purposes. Some species form pairs during reproduction, and others form complicated social groups. Some of these fishes build nests, and others lay eggs among plants. Some larvae, the early stage of an animal that must change form before becoming an adult, feed on eggs laid in another batch. Some males guard the young. Males of one type of knifefish hold the eggs in their mouths until the eggs hatch.

SOUTH AMERICAN KNIFEFISHES, ELECTRIC EELS, AND PEOPLE

Electric eels are used to study how electricity relates to biology. Some larger knifefishes are eaten by people who live in their geographic range.

CONSERVATION STATUS

South American knifefishes and electric eels are not threatened or endangered.

ELECTRIC EEL (Electrophorus electricus): SPECIES ACCOUNTS

Physical characteristics: Electric eels can reach a length of 8 feet (2.4 meters). They have no dorsal, tail, or pelvic fins and do not have scales. The bottom part of the head and throat is yellowish to orange, and the rest of the body is dull olive to almost black. These fishes produce electric discharges as strong as 700 volts.

Geographic range: Electric eels live in northern South America.

Habitat: Electric eels live in creeks and ponds and along the shores of lakes.

Diet: Electric eels eat mostly other fishes, but they also eat amphibians (am-FIB-ee-uns), such as frogs, which spend part of their lives in water and part on land.

Behavior and reproduction: Electric eels are active at night. They stun prey or food animals with electric shocks. These eels drown if they cannot get access to air, so they swim to the surface every ten minutes or so to gulp air. They hide during the day under shelter or in holes. Electric eels breed during the dry season in small ponds. The male builds a foam nest. The larvae first eat eggs of later spawnings, then change their diet to insect larvae. These eels start eating fish when they are about 4 inches (10 centimeters) long. The males guard the young until they can eat fish.

Electric eels and people: Electric eels have been used to study how electricity works in biology.

Conservation status: Electric eels are not threatened or endangered. ∎

GLASS KNIFEFISH (Eigenmannia lineata): SPECIES ACCOUNTS

Physical characteristics: Female glass knifefishes are about 8 inches (20 centimeters) long. Males are about 14 inches (36 centimeters) long. Their bodies are slender, having only pectoral fins (PECK-ter-uhl) fins, or the front pair, and a very long anal fin. Except for the head, the fish are clear. Three black stripes run lengthwise along the body. Glass knifefishes are weakly electric.

Geographic range: Glass knifefishes live in South America.

Habitat: Glass knifefishes live near undercut banks and in old wood along rivers and streams; in the open-water areas of small creeks, lagoons, and marshes; and along rivers with dense plant life.

Diet: Glass knifefishes eat crustaceans and the larvae of water insects.

Behavior and reproduction: Glass knifefishes are social and are active at night. During the day they gather in large numbers in hiding places. They spawn during the rainy season. The dominant male spawns with a female at night, and she lays sticky eggs on floating plants. The eggs hatch on the third day after being laid.

Glass knifefishes and people: Glass knifefishes are studied by scientists.

Conservation status: Glass knifefishes are not threatened or endangered. ∎

FOR MORE INFORMATION

Books:

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

Web sites:

"Electric Eel." All Science Fair Projects. http://www.all-science-fair-projects.com/science_fair_projects_encyclopedia/Electric_eel (accessed on September 26, 2004).