Anableps, called colloquially the four-eyed fish, does not actually have four eyes. Its eyes only appear divided, split horizontally into two sections by a band of tissue, which makes it seem to have four eyes. This surface-dwelling fish makes good use of this feature to see above and below the water. It can search for food below the surface and keep an eye on predators above at the same time. Anableps rarely leave the surface. This fish is even known to leap onto sandbanks to snatch terrestrial insects.
Common Names: Four-eyed fish, largescale foureyes, stargazer, cuatro-ojos, and striped foureyed fish
Scientific Name: Anableps anableps
Adult Size: 12 inches (30 centimeters)
Life Expectancy: 6 to 8 years
|Origin||The north-east South American coastline from the Gulf of Paria through Guyana, Suriname, and French Guiana and past the Amazon delta in Brazil|
|Tank Size||65 gallon|
|Diet||Primarily a carnivore, but needs a varied diet|
|pH||7.0 to 8.5|
|Hardness||10 to 25 dGH|
|Temperature||75 to 87 F|
Origin and Distribution
Anableps are found along the Atlantic coast of Central and South America and around the island of Trinidad. Its favored habitat consists of river estuaries and surrounding mangrove swamps where the water is brackish, with salinity changing with the ebb and flow of the tide.
Colors and Markings
Their generally cylindrical body has an olive-brown-colored dorsal surface. The flanks and belly are a light cream color with four narrow parallel dark stripes beginning behind the large pectoral fins decorating the flanks. The most noticeable feature of this fish is its two large, bulbous eyes that protrude from a small head.
These four-eyed fish are peaceful but will eat fish that are small enough to fit into their mouths. They are a schooling fish and must be kept in groups of six or more. Other fish suitable for a brackish tank could include archerfish or monos. Alternative aquarium choices for the brackish aquarium are some colorful sailfin mollies or even a group of orange chromide cichlids, which would occupy a different zone of the aquarium.
Anableps Habitat and Care
As these are surface-swimming fish, the water level in the aquarium needs to be dropped 12 inches from the top but the water should be at least 12 inches deep, dictating an aquarium with a height of 24 inches. Four-eyed fish are good jumpers, so the aquarium needs a tight-fitting cover.
The aquarium bottom should be furnished with a 3-inch gravel bed that can be overlaid with some smooth rocks or even bogwood. However, a large water surface should be maintained for the four-eyed fish. Additionally, regular partial water changes (20 percent) with new brackish water are needed every two weeks to remove accumulating nitrates and to maintain good water quality.
Anableps Diet and Feeding
The four-eyed fish greatly appreciates live insects found at the water's surface. In the wild, their diet consists mostly of insects and small crabs, but they also consume small fish, other invertebrates, diatoms, amphipods, snails, mussels, and worms in smaller amounts.
In the aquarium, they will gladly eat floating food sticks, pellets, flake foods, and freeze-dried foods and will especially enjoy live insects as large as crickets. Live or frozen foods, such as brine shrimp, bloodworms, and tubifex worms, as well as daphnia can be offered to vary their diet. All these various types of foods are generally taken at or near the water surface.
Females anableps are larger than the males. In the wild, the females can reach almost 12 inches in length while the males reach just shy of 8 inches. In the aquarium, females generally reach a length of only about 10 inches. These fish become sexually mature at about 8 months of age or when they have reached a length of 6 inches.
As the male fish matures, the anal fin becomes modified into a narrow sex organ called a gonopodium. It is pipe-shaped, greatly elongated, and fused into a tube. The Anableps species are one-sided livebearers; on these fish types, the male gonopodium and the female genital aperture are located either on the right or left side. To mate, they must pair with a member of the opposite sex that is sexually adorned on the compatible side.
Breeding the Anableps
Four-eyed fish will usually mate and produce live young without the need for any special setups. Providing that the group is sexually mature and includes healthy males and females that are sexually compatible with each other, breeding will occur. The male will approach the female from behind, repeatedly pushing against her to stimulate mating.
The four-eyed fish are livebearers in which developing embryos undergo gestation inside the female fish. Here, each developing embryo is nourished principally through the embryo’s expanded belly sac, the surface of which is covered with delicate blood vessels, which can absorb nutrients and oxygen from the mother’s blood supply, while wastes, metabolites, and carbon dioxide from the embryo are carried away by the mother’s blood supply, just as in humans.
The gestation period of about eight weeks is dependent on the temperature of the water and usually results in 10 to 15 large fry that are already 2 to 2.8 inches when the female drops them, usually tail first.
The fry, which are miniature copies of the female fish, may be eaten by other fish in the aquarium, so they should be moved to their own tank that contains similar conditions to the main aquarium. The fry will grow quickly if they are well-fed with small live food, such as fruit flies, bloodworms, and daphnia, as well as flakes and small floating pellets. Male and female young four-eyed fish are initially identical, but eventually, the male’s anal fin develops into a gonopodium, while females grow faster and are eventually larger than males. The ratio of male to female fry is usually one to one.
More Pet Fish Species and Further Research
If the four-eyed anableps appeals to you, and you are interested in similar fish for your brackish aquarium, check out:
Check out additional fish species profiles for more information on other freshwater fish.