Why do flounders have eyes on only one side?

The reason why the flatfish has two eyes on one side is because it has gradually adapted to the environment over a long period of time.

When it hatches from an egg into a small fish, like other small fish, its two eyes are symmetrically placed on both sides of its head. However, when it grows about 20 days and its body grows to 1 cm long, due to the uneven development of its body parts, it gradually turns its body sideways when swimming, and begins to live on the seabed lying on its side. At the same time, the eye on the lower side of it moves upward due to the continuous growth of the soft band under the eye, passing through the spine and reaching the top, and is parallel to the original eye on the top. When it moves to the appropriate position, the orbital bone of the moving eye is formed and no longer moves and becomes fixed. Flatfish with a twisted mouth and one eye on one side. Shark's Nemesis - Flatfish Flatfish is the shark's nemesis because it can secrete a milky white liquid toxin. When a shark swims close to a flatfish and is about to open its mouth to swallow it, the flatfish will quickly secrete milky white venom. When the shark's mouth comes into contact with the venom, the jaw muscles are immediately paralyzed by the venom, and the shark's bloody mouth cannot be closed, so it has to swim away in disgrace.

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