Four-Eyed Fish Care Guide - Aquarium Setup, Diet & Breeding

Four-Eyed Fish are among the most unusual aquarium fish, named for their remarkable eyes. Each eye is divided into upper and lower sections by a horizontal band of tissue, allowing the fish to see above and below the waterline at the same time. The upper portion is adapted to viewing air, while the lower portion is suited to seeing underwater.

Four-Eyed Fish of the genus Anableps are native to tropical coastal waters, tidal creeks, mangrove zones and estuaries of Central and South America. They occur from Mexico and Central America southward through northern South America, including parts of Brazil, and may be found in fresh, brackish and mildly marine-influenced habitats.

A group requires at least 200 litres, with a long aquarium measuring about 120 cm by 45 cm or larger; surface area is more important than height. Use a secure cover because these fish are powerful surface swimmers and can jump. Provide open swimming space, gentle filtration with good oxygenation, and a stable, hard, alkaline setup that may be maintained as freshwater or mildly brackish according to the species and source. Add smooth sand or fine gravel, sturdy marginal plants, floating cover and driftwood or rock around the edges, while leaving much of the surface unobstructed for feeding.

Females can reach about 30 cm (12 in) in total length, while males are usually smaller at around 20–25 cm (8–10 in). Aquarium specimens are often somewhat smaller than the largest wild females.

Four-Eyed Fish are surface-feeding omnivores with a strong preference for insects and other small prey. Offer floating pellets or flakes alongside appropriately sized frozen or live foods such as bloodworms, brine shrimp, mysis shrimp, mosquito larvae and small crustaceans. Small insects, including flightless fruit flies, can provide useful enrichment, but avoid collecting food from polluted areas. Feed modest portions that are eaten quickly at the surface.

Four-Eyed Fish are generally peaceful toward fish of similar size but can be assertive with one another, especially when space is limited. Suitable tankmates include robust, peaceful brackish species such as monos, scats and larger livebearers, provided their water requirements match. Avoid tiny fish, slow-moving species, fin-nippers and aggressive tankmates, as well as fish that compete heavily at the surface. They should not be mixed casually with delicate community fish that require soft, acidic freshwater.

Four-Eyed Fish are livebearers and are usually bred by keeping a compatible male and female together in mature, spacious water. Mating is influenced by the male’s one-sided gonopodium, so males and females must be oriented compatibly. After roughly two months of gestation, the female gives birth to relatively large, fully formed young. Provide dense floating cover or a separate birthing area, as adults may eat the fry; newly born fish can take small live or frozen foods and finely crushed prepared food.

Females are noticeably larger and heavier-bodied than males. Males possess a prominent gonopodium, a modified anal fin used for internal fertilisation, while females have a normal fan-shaped anal fin and lack this reproductive organ.