Four-eyed fishes - strange pets

By Sophie Kininmonth · 5 Oct 2025 (updated 21 Jul 2026) ·6 min read

Four-eyed fish (genus Anableps) are surface specialists that look like they are watching two worlds at once, and in a sense they are. Despite the name they have two eyes, not four, but each eye is split so the top half sees through air and the bottom half sees underwater at the same time.^{1, 2} They are active, sociable fish from the estuaries and mangrove edges of northern South America, and they make a genuinely fascinating display animal for the right tank. They are also an exotic brackish species, so before you plan a tank, check that they are legal to keep where you live: ownership of non-native fish in Australia depends on state and territory law, and you should confirm with your state fisheries or biosecurity authority first.

Quick facts (at a glance)

Common name: Four-eyed fish (often "largescale foureyes")
Scientific name: Anableps anableps (most commonly kept), genus Anableps¹
Adult size: up to about 30 cm total length (commonly smaller)^{1, 3}
Natural habitat: estuaries, coastal lagoons, mangrove shorelines; fresh to brackish water^{3, 4}
Diet: insects and other invertebrates; also small fish and other foods depending on opportunity^{3, 4}
Social behaviour: often seen schooling, especially when young⁶
Reproduction: livebearer (internal fertilisation), not an egg-layer^{7, 8}
Special consideration: needs a tight-fitting lid; surface fish that can launch themselves out of gaps

What are four-eyed fish?

Four-eyed fish are surface specialists from the Neotropics, from places where river water meets the sea and tides push through mangroves and mudflats. The genus is Anableps, and the best-known species in the aquarium trade is Anableps anableps.^{1, 3} They spend much of their time right at the waterline, holding it across their eyes. That posture is the whole trick: each eye is divided so the upper portion is tuned for air vision and the lower portion for underwater vision, letting the fish track movement in both worlds at once.^{1, 2}

The "four eyes" explained

The name oversells it slightly. An Anableps has two eyes, each divided internally and externally into an upper and lower half, with anatomical tweaks that help form useful images in air and in water at the same time.^{1, 2} In anatomical descriptions the split includes features such as two pupils within each eye, plus differences in corneal and lens shape between the aerial and aquatic halves. It is a neat solution to the optical problem created by the air and water boundary.^{2, 5}

Natural range and habitat

Anableps anableps is recorded from northern South America, including Trinidad and the mainland coast from Venezuela through to the Amazon delta region. It is closely tied to lowland coastal waters, the estuaries, lagoons and mangrove edges where salinity swings with tides and rain.^{3, 4} That background matters in captivity. These fish are not stream-dwellers in the usual freshwater community tank sense; they are built for broad, shallow, changeable places where the surface is the main stage.

Temperament and group dynamics

Four-eyed fish are sociable. In the wild they are often seen in groups, and juveniles can gather in sizeable schools.⁶ In an aquarium they are generally best treated as social fish, so keeping a small group spreads attention around and reduces the intensity of dominance displays. They are also energetic, surface-oriented cruisers. A cramped tank does not just limit swimming space, it forces constant close contact at the surface, which is exactly where they naturally spend most of their time.

Tank setup that suits their biology

Tank size and shape

Length matters more than height. Because Anableps can reach around 30 cm and are persistent surface swimmers, a long aquarium gives them room to move without repeatedly colliding, turning and jostling at the same patch of surface.^{1, 3}

Cover and escape prevention

Plan for a tight-fitting lid and block small gaps around hoses and cables. Surface fish accelerate quickly, and a startled individual can clear the waterline in a single burst. Treat the lid as essential equipment, not an optional extra.

Fresh vs brackish water

In nature Anableps anableps is associated with both fresh and brackish environments, commonly linked to coastal lagoons and mangrove shorelines where salinity varies with tides.^{3, 4} Many aquarists therefore keep them in brackish conditions to better match typical habitat. If you choose brackish water, change salinity gradually and keep it stable once set.

Temperature and water quality

They are tropical fish and are commonly listed around the mid-20s degrees Celsius as typical.³ More important than chasing one perfect number is steady temperature, strong filtration and consistent maintenance, especially because these fish eat eagerly and produce a fair amount of waste for their time at the surface.

Feeding: what they eat and how they hunt

Anableps feed on insects and other small invertebrates, and may also take small fish and other foods depending on what is available.^{3, 4} In an aquarium this translates well to a varied diet built around quality prepared foods plus frozen or live options. They are set up to notice movement above the surface, so floating foods and surface feeding become a regular part of their routine. Keep an eye on tankmates, because slow feeders can be outcompeted when an Anableps group is in feeding mode.

Compatibility: choosing tankmates carefully

Four-eyed fish occupy the surface almost constantly, and that alone narrows the guest list. Avoid other surface specialists that will compete at the same layer, and avoid nippy species that target fins. If you keep tankmates, aim for peaceful fish that prefer mid-water or the bottom and that tolerate the same fresh-to-brackish conditions you are running. Watch for subtle stress signals such as frayed fins, clamped posture, or fish refusing to use open water, and adjust before it becomes chronic.

Breeding basics

Four-eyed fish in the family Anablepidae, including Anableps, are livebearers. They use internal fertilisation, and females give birth to live young rather than laying eggs that are fertilised externally in the water.^{7, 8} There is a further twist: in Anableps anableps the genital opening and the male's gonopodium can be oriented to the left or the right, and successful mating generally requires compatible handedness.^{8, 9}

Legality and buying in Australia

Legality comes first. Four-eyed fish are an exotic, non-native brackish species, and whether you can legally import or keep them in Australia depends on your state or territory law. Confirm the rules with your state fisheries or biosecurity authority before you buy. If they are permitted where you live, look for specialist aquarium shops with experience in brackish species and a track record of selling robust, well-acclimated fish. Ask what salinity and temperature the fish are currently kept in, and match those conditions closely during quarantine and acclimation. Avoid impulse purchases from sources that cannot tell you the water parameters.

The bottom line

Four-eyed fish reward patient keepers who build a tank around how the species actually lives: a long surface runway, stable water and a lid that leaves no doubt. Get that foundation right, and check the legalities for your state first, and you will see the quiet, constant scanning that makes Anableps so distinctive, half in one world and half in the other with the waterline drawn straight through their gaze.^{1, 2}

References

Sophie Kininmonth

Dog lover and writer at My Pets Australia, sharing practical breed guides and care advice for Australian pet owners.