The ling, turbot, brill, dog fish live entirely upon small fish. The dog fish swarms on certain fishing grounds and is often a serious pest to the drift-net fishermen, destroying their nets as well as the fish that are attached to them.
The whiting, like the cod, feeds upon small fish, and upon crustacea and mollusca.
The food of the haddock consists of mollusca, crustacea and marine worms, etc.
The sole lives on small crustacea, for example shrimps, and marine worms.
Skates and rays feed upon mollusca and crustacea.
Most shellfish live in shallow water and feed upon the plankton.
The methods by which fish obtain their food differ greatly according to the species of the fish. Pelagic fish, e.g. herring and mackerel, sprat and pilchard, obtain their food almost automatically as they swim open-mouthed through the water in which it abounds. These direct plankton-feeders possess comb-like structures—the gill-rakers—attached behind the gill openings, and as the food-bearing water streams through the mouth and gill openings of the fish, these structures strain the food from it. The fish licks the plankton from its gill-rakers with its tongue and swallows it.
Many pelagic fish, e.g. carp, trout, salmon, look for their food while swimming through the well-lighted surface water.
Demersal fish—flat fish, cod, haddock, etc.—seek their food by scent and touch. The cod possesses a barbel attached to its chin, by means of which it feels for its food.