The flounder – Pseudopleuronectes – is the collective name of several species belonging to the suborder Pleuronedctidae, widespread especially in the coastal areas in the Pacific and the Atlantic.
All species of flounders look very similar in terms of shape, but they vary significantly in terms of size – they can be of any size from 22 cm to over 90 cm and they can weigh up to 9 kg (20 pounds). They all have flat, round-shaped bodies with tail fins, and they are all colored to help them blend into the sea floor, where they spend most of their time.
Flounders are greyish, but they have a very peculiar feature that distinguishes them from any other fish: the migrating eye. After hatching, flounders have one eye on each side of their head, but by the time they reach adulthood, this bilateral symmetry disappears and one of the eyes migrates to the other side. So, fully developed flounders have both their eyes located on the same side of their head. The reason for this strange migration is that the adult animal is larger, and therefore it needs to bury itself deeper into the sand. Flounders bury themselves lying on one side and they can get maximum visibility over the area around them if they have both eyes looking the same direction. The side where the eyes are on depends on the species. As flounders spend most of their life buried on their bellies in the sand – the belly loses its coloring gradually, colors appearing only on the side where the eyes are.
Flounders feed mainly on small invertebrates such as crustaceans, on small fish and on fish spawn. They are predators, getting their food hiding in the soft sea bed and ambushing their prey – they wait motionless, buried in the sand, with only their eyes protruding, until their prey comes swimming by. Then they just leap out of their hiding place and grab their victim. They are known to be voracious predators.
Flounders proliferate by means of spawning. The female releases her eggs into the water, while the male releases his sperm to fertilize the eggs. The fertilized eggs then disperse through the water column and hatch into flounder (Pseudopleuronectes) larvae.