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Flat Fish :: Food and Beverage Service :: Semester II :: FYCT/ FYBSc

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FISHES :: Flat fish

The flatfish are an order of ray-finned fish, also called the Heterosomata, sometimes classified as a suborder of

Perciformes. The name means "side-swimmers" in Greek. In many species, both eyes lie on one side of thehead, one or the other migrating through and around the head during development. Some species face their

left side upward, some face their right side upward, and others face either side upward.

Many important food fish are in this order, including the flounders, soles, turbot, plaice, and halibut. There are

more than 400 species of this order. Some flatfish can camouflage themselves on the ocean floor.

The most obvious characteristic of the flatfish is their asymmetry,

with both eyes lying on the same side of the head in the adult fish.

In some families, the eyes are always on the right side of the body,and in others, they are always on the left. The primitive spiny

turbots include equal numbers of right and left sided individuals,

and are generally less asymmetrical than the other families. Other

distinguishing features of the order are the presence of protrusible

eyes, another adaptation to living on the seabed, and the

extension of the dorsal fin onto the head.

The surface

of the fish facing away from the sea floor is pigmented,

often serving to camouflage the fish, but sometimes with

striking colored patterns. Some flatfish are also able to

change their pigmentation to

match the background, in a manner similar

to a chameleon. The side of the body without the eyes, which faces

the seabed, is usually colorless or very pale.

The flounders and spiny turbots eat smaller fish, and havewell-developed teeth. They sometimes seek prey in the mid-

water, away from the bottom, and show less extreme adaptations

than other families. The soles, by contrast, are almost exclusively bottom dwellers, and feed

on invertebrates. They show a more extreme asymmetry, and may lack teeth on one side of the jaw.

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Flat Fish :: Food and Beverage Service :: Semester II :: FYCT/ FYBSc

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Flatfish lay eggs that hatch into larvae resembling typical

symmetrical, fish. These are initially elongated, but

quickly develop into a more rounded form. The larvae

typically have protective spines on the head, over the

gills, and in the pelvic and pectoral fins. They also

possess a swim bladder, and do not dwell on the bottom,

instead dispersing from their hatching grounds as

plankton.

The length of the planktonic stage varies between

different types of flatfish, but eventually they begin to metamorphose into the adult form. One of the eyes

migrates across the top of the head and onto the other side of the body, leaving the fish blind on one side. The

larva also loses its swim bladder and spines, and sinks to the bottom, laying its blind side on the underlying

surface.