Speaking of flounder, in addition to being able to eat, what is more attractive is its squeezed eyes on one side.
The eyes of ordinary fish are on both sides of the head, so how did this guy grow crooked?
"Eyes on the same side" are not born that way
The flounder larvae that have just hatched from the egg membrane do not resemble their parents at all, and are very similar to ordinary fish. Eyes grow on either side of the head. One on each side, arranged symmetrically.
They live in the upper layers of the water and often swim near the surface of the water.
After about 20 days, something magical began to happen: the flounder larval morphology began to change. When the flounder's larvae grow to 1 cm, the eyes on one side of the flounder begin to move.
It gradually moves to the opposite side through the upper edge of the head, and does not stop moving until it is close to the other eye. Different species of flounder eyes move differently in terms of methods and routes. The skull of a flounder is made of cartilage. When the flounder's eyes begin to move, the cartilage between the flounder's eyes is first absorbed by the body.
In this way, the obstacle to eye movement is cleared. As the eyes of the flounder move, the internal structure and organs of the flounder change accordingly.
Flounder abandons floating life and gradually lies on the bottom of the sea.
Why is there such a change?
It can be said that it is the result of natural selection and the process of its own evolution.
Flounders usually swim sideways, and they often lie flat on the ocean floor, covered with a layer of sand. For predation and to spot enemies faster, having two eyes together is undoubtedly the best option.
Of course, scientists have discovered genes and mechanisms for eye transfer in flounders:
(The scientific name of the partial mouth fish is flounder, which is a general term for the flounders of the teleost fish family, including turbots, flounders, rays, and tongue rays.) Turbot brown and semi-slippery tonguefish began to differentiate 70 million years ago, but their genomes are as similar as 85% and have up to 15,534 homologous genes. ）
The research team led by Chen Songlin of qingdao National Laboratory for Marine Science and Technology marine fisheries science and food production process and researchers from the Yellow Sea Fisheries Research Institute and researchers from Shanghai Ocean University, Würzburg University in Germany, Algarve University in Portugal, Shenzhen Huada Gene Research Institute and other units jointly deciphered the whole genome sequence of brown turbot, and through comparative analysis with the whole genome of semi-slippery tongue fish, the molecular mechanism of flounder metamorphosis was initially revealed.
The results were published in Nature-Genetics on December 5, 2016.
Based on the homologous genes screened by brown turbot and semi-slippery tongue trout at different stages of metamorphosis, expert experiments have found that retinoic acid and thyroid hormones can inhibit brown turbot eye movement.
(The pictures are from the Internet, and the infringement must be deleted)