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.