Four-eyed fish
Encyclopedia
The four-eyed fishes are a genus, Anableps, of fish
es 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. Like their relatives, the onesided livebearer
s, four-eyed fishes only mate on one side, right-"handed" males with left-"handed" females and vice versa. These fish inhabitat freshwater
and brackishwater and are only rarely coastal marine
. They originate from lowlands in southern Mexico
to Honduras
and northern South America
.
s which are readily available at the surface, however they may consume other foods such as other invertebrate
s, diatom
s, and small fishes.
These fish will group differently depending on the species. A. anableps commonly congegrates in schools
. A. microlepis also is gregarious, but restricts its schools to about a dozen individuals; it is also recorded to be found singly or as couples.
A. anableps is also known for the ability to survive out of water exposed to air, such as during low tide.
in A. microlepis, making this species the largest in the order Cyprinidontiformes.
s, connected by part of the iris
. The upper half of the eye is adapted for vision in air, the lower half for vision in water. The lens of the eye also changes in thickness top to bottom to account for the difference in the refractive indices
of air versus water.
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
es in the family Anablepidae
Anablepidae
Anablepidae is a family of freshwater and brackish water fishes living on river estuaries from southern Mexico to southern South America. There are three genera with sixteen species: the four-eyed fishes , the onesided livebearers and the white-eye, Oxyzygonectes dovii...
. 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. Like their relatives, the onesided livebearer
Onesided livebearer
Jenynsia is a genus of freshwater fishes in the family Anablepidae. Like Anableps species, they are onesided livebearers: some sources indicate that they only mate on one side, right-"handed" males with left-"handed" females and vice versa. However other sources dispute this...
s, four-eyed fishes only mate on one side, right-"handed" males with left-"handed" females and vice versa. These fish inhabitat freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
and brackishwater and are only rarely coastal marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
. They originate from lowlands in southern Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
to Honduras
Honduras
Honduras is a republic in Central America. It was previously known as Spanish Honduras to differentiate it from British Honduras, which became the modern-day state of Belize...
and northern South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
.
Behavior
These fish spend most of their time at the surface of the water. Their diet mostly consists of terrestrial insectInsect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s which are readily available at the surface, however they may consume other foods such as other invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, diatom
Diatom
Diatoms are a major group of algae, and are one of the most common types of phytoplankton. Most diatoms are unicellular, although they can exist as colonies in the shape of filaments or ribbons , fans , zigzags , or stellate colonies . Diatoms are producers within the food chain...
s, and small fishes.
These fish will group differently depending on the species. A. anableps commonly congegrates in schools
Shoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
. A. microlepis also is gregarious, but restricts its schools to about a dozen individuals; it is also recorded to be found singly or as couples.
A. anableps is also known for the ability to survive out of water exposed to air, such as during low tide.
Physical characteristics
The maximum length of these species is up to 32 cm TLFish measurement
Fish measurement refers to the measuring of the length of individual fish and of various parts of their anatomy. These data are used in many areas of ichthyology, including taxonomy and fisheries biology.-Overall length:...
in A. microlepis, making this species the largest in the order Cyprinidontiformes.
Reproductive organs
These fish are one-sided livebearers and their reproductive organs are unique to its subfamily. This characteristic is only shared with the related genus Jenynsia.Eye
The four-eyed fishes only have two eyes each, but the eyes are specially adapted for their surface-dwelling lifestyle. The eyes are positioned on the top of the head, and the fish floats at the water surface with only the lower half of each eye underwater. The two halves are divided by a band of tissue and the eye has two pupilPupil
The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...
s, connected by part of the iris
Iris (anatomy)
The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...
. The upper half of the eye is adapted for vision in air, the lower half for vision in water. The lens of the eye also changes in thickness top to bottom to account for the difference in the refractive indices
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
of air versus water.