Flat Fish -- a Prime Example of Evolution

Back around U.E. 1054820687 (almost a decade ago), our family attended a (Chinese) feast hosted by my aunt and her family. I don't exactly remember the occasion but there was a vivid memory. One of the items was a fish, which had one of its eyes on top of its head.

Like this.

Although it was a bit scary for us, kids (it has sharp teeth too), it was a delicious dish. We asked my uncle what fish it is and he replied it was flat-fish (yeah, direct translation from our language is also flat-fish). Therefore, my mom started to buy and cook flat-fish for us frequently. 

Once, I asked my mother how to find the un-cooked flat-fish in the market -- what are its features and she replied, "It's black on a side and white on the other." I couldn't believe my ears (the Chinese recipe put dark soy sauce on both side of the fish so when it was on the plate the color were even). To my amazement, the next time I went to market with my mom, she showed me the black-one-a-side-white-on-the-other horror.

They are commonly called "Sole Fish" around the world. Today I browse the internet and learned why their eyes are like that and their body color is that way.Their scientific classification is Kingdom: Animalia, Phylum: Chordata, Class: Actinopterygii, Order: Pleuronectiformes. Well, Kingdom and Phylum are not important :D

Their traits include dwelling on the seabed on one side, camouflaging like Chameleons and having protrusible eyes, i.e. their eyes can come out of the sockets. Like many natural phenomenons, their strange appearances have scientific explanation. Let me quote Richard Dawkins:

…bony fish as a rule have a marked tendency to be flattened in a vertical direction…. It was natural, therefore, that when the ancestors of [flatfish] took to the sea bottom, they should have lain on one side…. But this raised the problem that one eye was always looking down into the sand and was effectively useless. In evolution this problem was solved by the lower eye ‘moving’ round to the upper side.

So, the problem is solved. They need to hide on the seabed so they can't swim like normal fishes; they must lie on their sides and swim in an awkward way. Therefore, the side that faces upward (towards the air) must have color similar to the seabed to hide while the other side (facing downward (towards the earth) can have arbitrary color. That's why it is one side black and the other white (pale). For the eyes, the quote above has a very good explanation.

Logged on Doughnut I/O. U.E. 1338905081.