Anableps anableps

Anableps anableps
	at Caroni Swamp, Trinidad
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Cyprinodontiformes
Family:	Anablepidae
Genus:	Anableps
Species:	A. anableps
Binomial name
	Anableps anableps; (Linnaeus, 1758)
Synonyms[1]
	Cobitis anableps Linnaeus, 1758; Anableps anableps Meuschen, 1778; Anableps tetrophthalmus Bloch, 1794; Anableps surinamensis Lacepède, 1803; Anableps gronovii Valenciennes, 1846; Anableps lineatus Gronow, 1854;

Anableps anableps, the largescale four-eyes,[2] is a species of four-eyed fish found in fresh and brackish waters of northern South America and Trinidad. This species grows to a length of 30 centimetres (12 in) TL. This fish can occasionally be found in the aquarium trade. The fish does not actually have four eyes, but instead each eye is split into two lobes by a horizontal band of tissue, with each lobe having its own pupil and separate vision. This allows the fish to see under and above the surface of the water at the same time.[1]

Taxonomy

Largescale four-eyed fish at Hellabrunn Zoo

This fish was first described in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his Systema Naturae. Linnaeus gave it the name Cobitis anableps, but it was later transferred to the genus Anableps, becoming Anableps anableps.[3]

Description

Anableps anableps is a slender elongate fish that can reach 30 cm (12 in). Male fish have the anal fin modified into an intromittent organ 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 longitudinally and thus has two pupils; the fish positions itself in the water in such a way that the dividing line rests on the surface of the water, with one pupil in the air while the other is submerged.[4]

Distribution and habitat

Anableps anableps is found in the tropical western Atlantic Ocean and the southern Caribbean Sea. Its range extends from Trinidad and Venezuela to the delta of the Amazon River in Brazil. It mostly occurs in estuaries and on coastal mudflats, but it can survive in fresh water environments for extended periods.[4]

Ecology

Anableps anableps feeds on insects and other small invertebrates 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 diatoms found among the grains.[4] 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 day-light spring tides and was at its minimum at night-time neap tides, 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.[5]

In the water, this fish uses a combination of biting and suction to capture its prey. It sometimes emerges from the water and feeds on mudbanks,[2] but a fish's 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.[2]

This fish has internal fertilisation and bears live young.[4]

References

Froese, Rainer and Pauly, Daniel, eds. (2019). "Anableps anableps" in FishBase. August 2019 version.
Michel, Krijn B.; Aerts, Peter; Gibb, Alice C.; Van Wassenbergh, Sam (2015). "Functional morphology and kinematics of terrestrial feeding in the largescale foureyes (Anableps anableps)". Journal of Experimental Biology. 218: 2951–2960. doi:10.1242/jeb.124644.CS1 maint: multiple names: authors list (link)
Bailly, Nicolas (2020). "Anableps anableps (Linnaeus, 1758)". WoRMS. World Register of Marine Species. Retrieved 26 January 2021.
Reis, Roberto E.; Kullander, Sven O.; Ferraris, Carl J. (2003). Check List of the Freshwater Fishes of South and Central America. EDIPUCRS. pp. 582–583. ISBN 978-85-7430-361-1.
Brenner, M.; Krumme, U. (2007). "Tidal migration and patterns in feeding of the four‐eyed fish Anableps anableps L. in a north Brazilian mangrove". Journal of Fish Biology. 70 (2): 406–427. doi:10.1111/j.1095-8649.2007.01313.x.CS1 maint: multiple names: authors list (link)

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[Fishbase-1] Froese, Rainer and Pauly, Daniel, eds. (2019). "Anableps anableps" in FishBase. August 2019 version.

[Krijn-2] Michel, Krijn B.; Aerts, Peter; Gibb, Alice C.; Van Wassenbergh, Sam (2015). "Functional morphology and kinematics of terrestrial feeding in the largescale foureyes (Anableps anableps)". Journal of Experimental Biology. 218: 2951–2960. doi:10.1242/jeb.124644.CS1 maint: multiple names: authors list (link)

[WoRMS-3] Bailly, Nicolas (2020). "Anableps anableps (Linnaeus, 1758)". WoRMS. World Register of Marine Species. Retrieved 26 January 2021.

[Reis-4] Reis, Roberto E.; Kullander, Sven O.; Ferraris, Carl J. (2003). Check List of the Freshwater Fishes of South and Central America. EDIPUCRS. pp. 582–583. ISBN 978-85-7430-361-1.

[5] Brenner, M.; Krumme, U. (2007). "Tidal migration and patterns in feeding of the four‐eyed fish Anableps anableps L. in a north Brazilian mangrove". Journal of Fish Biology. 70 (2): 406–427. doi:10.1111/j.1095-8649.2007.01313.x.CS1 maint: multiple names: authors list (link)