Well, you’d
be surprise to know, that there’s three recognized species which’ve four eyes.
However; a normal human being is well satisfied with two eyes. But sometimes
nature is unforeseen to unbelievable things. The unique four eyed fishes are a
genus, Anableps, of fishes belongs to the family of “Anablepidae”. They’ve 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. A. anableps is
also recognized for the skill to survive out of water exposed to air, such as
during low tide.
Like their
relatives, the one-sided livebearers, four-eyed fishes only mate on one side,
right-"handed" males with left-"handed" females and vice
versa. These fish inhabit freshwater and brackishwater and are only rarely
coastal marine. They originate from lowlands in southern Mexico to Honduras and
northern South America. There’re presently three recognized species in this
genus, which are Anableps anableps (Largescale foureyes), Anableps dowei
(Pacific foureyed fish), and Anableps microlepis (Foureyes).
These
fishes like to spend most of their time at the surface of the water, and they
like to eat mostly terrestrial insects which’re readily available at the
surface; though their foods also consist of other foods such as other
invertebrates, diatoms, and small fishes. Interestingly these fish will group
contrarily depending on the species. A. anableps usually congregates 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. These
fish have an exclusive anatomy for reproduction. Because four eyed fish have
sex organs that’re either turned to the left or to the right side of their
body. Hence, a “left” male can only mate with a “right” female and vice versa.
They give birth to live young
In the
physical characteristics, these species have maximum length of upto 32 cm TL in
A. microlepis, making this species the largest in the order Cyprinidontiformes.
Although these fish are one-sided livebearers and their reproductive organs are
exclusive to its subfamily, and their characteristic is only shared with the
related genus Jenynsia. The unique four-eyed fishes only have two eyes each,
but the eyes are particularly adapted for their surface-dwelling lifestyle.
The
eyes are incredibly well positioned on the top of the head, which can fish make
floats at the water surface with only the lower half of each eye underwater.
Whereas the two halves are well divided by a band of tissue and the eye has two
pupils, linked by part of the iris, and the upper half of the eye is adapted
for vision in air, the lower half for vision in water. Hence; the lens of the
eye also changes in thickness top to bottom to account for the dissimilarity in
the refractive indices of air versus water. Source: Charismatic Planet