''Anableps anableps'', the largescale four-eyes, is a species of

four-eyed fish The four-eyed fishes are a genus, ''Anableps'', of fishes in the family Anablepidae. They have eyes raised above the top of the head and divided in two different parts, so that they can see below and above the water surface at the same time. Lik ...

found in fresh and brackish waters of northern

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

and

Trinidad Trinidad is the larger and more populous of the two major islands of Trinidad and Tobago. The island lies off the northeastern coast of Venezuela and sits on the continental shelf of South America. It is often referred to as the southernmos ...

. This species grows to a length of TL. This fish can occasionally be found in the

aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...

trade. The fish does not actually have four eyes, but instead each eye is split into two lobes by a horizontal band of tissue, each lobe with its own pupil and separate vision. This allows the fish to see above and below the surface of the water at the same time.

Taxonomy

This fish was first described in 1758 by the Swedish naturalist

Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

in the tenth edition of his ''

Systema Naturae ' (originally in Latin written ' with the ligature æ) is one of the major works of the Swedish botanist, zoologist and physician Carl Linnaeus (1707–1778) and introduced the Linnaean taxonomy. Although the system, now known as binomial nomen ...

''. Linnaeus gave it the name ''Cobitis anableps'', but it was later transferred to the genus '' Anableps'', becoming ''Anableps anableps''.

Description

''Anableps anableps'' is a slender elongate fish that can reach . Male fish have the anal fin modified into an

intromittent organ An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs e ...

with the tip angled to one side. Female fish have a flap of skin covering either the left or right genital opening. The most distinctive feature of this fish is the eyes, which project prominently from the head. Each eye is divided lengthwise and thus has two pupils; the fish positions itself in such a way that the dividing line between the two parts of the eye lies on the surface of the water, so that one pupil has an aerial view while the other is submerged.

Distribution and habitat

''Anableps anableps'' is found in the tropical western Atlantic Ocean and the southern Caribbean Sea. Its range extends from

and Venezuela to the delta of the

Amazon River The Amazon River (, ; es, Río Amazonas, pt, Rio Amazonas) in South America is the largest river by discharge volume of water in the world, and the disputed longest river system in the world in comparison to the Nile. The headwaters of t ...

in Brazil. It mostly occurs in estuaries and on coastal mudflats, but it can survive in freshwater environments for extended periods.

Ecology

''Anableps anableps'' feeds on insects and other small invertebrates, small fish, small crabs, and on algae. It has occasionally been observed catching insects in the air, but otherwise it ingests prey on or near the surface. It also ingests silt, consuming the

diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s found among the grains. In mangrove areas of Brazil, it has a migration pattern synchronized with the tides; as the tide rises it enters the intertidal channels, feeding in the inundated mangroves at high water, and retreating to the main channels as the tide ebbs. Feed consumption was at its greatest around high water during daylight

spring tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...

and was at its minimum at night-time

neap tides Neap is a small village in the east coast of the Mainland of the Shetland Islands, Scotland. Neap is situated at the end of the road from Brettabister Brettabister is a settlement on the island of Mainland Mainland is defined as "relatin ...

, perhaps demonstrating the importance of the split-level eyes. Red intertidal algae ('' Catenella'' sp.) was the main food item, supplemented by insects and shore crabs, family

Grapsidae The Grapsidae are a family of crabs known variously as marsh crabs, shore crabs, or talon crabs. The family has not been confirmed to form a monophyletic group and some taxa may belong in other families. They are found along the shore among rocks ...

. In the water, the fish uses a combination of biting and suction to capture its prey. It sometimes emerges from the water and feeds on mudbanks, but its mouth is not well adapted for picking up food from the surface on dry land. ''Anableps anableps'' solves this difficulty by depressing the lower jaw and protruding the upper jaw, and ingesting the prey by suction. If the prey is too large to swallow, it is gripped by the teeth, the upper jaw is retracted and the fish bites the prey. This cycle of protrusion and biting can be repeated until the prey is able to be swallowed. This fish has internal fertilisation and bears live young.

References

{{Taxonbar, from=Q5240255 Anablepidae Freshwater fish of South America Fish of French Guiana Fish of Guyana Fish of Suriname Fish of Trinidad and Tobago Fish described in 1758 Taxa named by Carl Linnaeus