You can predict a lot about the feeding habits and life-style of a fish simply by looking at its mouth. The angle the mouth is set on the head, the presence of barbels around the lips, the shape and size of the teeth and even the size of the mouth – all offer clues to the way the fish feeds and even the general kind of food it eats. All this gives invaluable information to anglers keen to ensure their baits reach the fish they are trying to catch.
Top or bottom?
Nevertheless, it’s worth bearing in mind that few fish are limited by their anatomy to just one kind of food. Most are generalists and can switch from one kind of feeding behaviour to another should their preferred food be scarce or unavailable. General purpose The carp is mainly a bottom feeder — its mouth is well adapted for browsing on the bottom. It uses the two pairs of barbels at its lips and the protrusible jaws to detect food and then suck it up. Normally you expect to find carp feeding on the bottom but, as many anglers can tell you, they take baits in mid water and they also come right to the surface for bread and other floating baits.
The roach, a bottom and mid water feeder, is also a generalist. It eats small free-swimming crustaceans such as daph-nia and sometimes takes food items from the surface. But the roach’s mouth, though its top lip protrudes slightly, is not extendible like that of the carp and it doesn’t have barbels.
Head down, tail up The bream is much more specialized for lake or river bed feeding, though it too can feed in mid-water. Its mouth extends into a broad tube for sucking out bloodworm, snails or mussels from the mud. A whole shoal may work its way along the bottom, every fish with head down and tail dimpling the surface in shallow water. Even the body shape, with the long-based, well-developed anal fin and the lower lobe of the tail fin longer than the upper, helps the head-down posture — normal swimming movements tip the head of the fish towards the bottom.
The tench also feeds almost exclusively on the bottom. Its upper lip, longer than the lower, enables it to root in the mud for bloodworm and other insect larvae. Surface feeders Fish that predominantly feed at the surface are not abundant in Britain, but one that does it successfully is the bleak. It has a strongly upturned mouth, with lips on the tip of the head – a tremendous advantage when taking near-surface crustaceans and insects. The rudd, another surface feeder, has an upturned mouth and protruding lower lip, used to suck in floating insects such as mayflies.
The dace feeds at the surface, but its mouth is sited at the extreme tip of the body – to catch surface insects it hunts head-up, tail-down – which may use up more energy than the bleak’s way of life. It too can feed in mid water and on the bottom. Barbels for bottom feeders The presence of barbels is a certain sign that the fish seeks much of its food on the bottom. These highly sensitive organs, which detect buried food, are associated with a mouth sited on the underside of the head. The gudgeon’s mouth, with two barbels, and that of the barbel itself, with four ‘whiskers’, clearly belong to bottom feeders. Large barbel have thick fleshy lips packed with a mass of taste cells for sampling food items (or an angler’s bait) long before the fish takes it into its mouth. Scavengers Barbels also form part of the feeding senses of the wels catfish. The upper pair (in front of the eyes) are extremely long and can detect and taste food well in front of the head. The wels’ mouth is huge and broad and can engulf large food items on the bottom. The eel, another general bottom-living predator and scavenger, has no barbels, but it does have an acutely sensitive sense of smell. In the eel too the mouth is large and its jaws have a dense patch of fine teeth. Predators Fish-eating predators — pike and zander — are clearly well equipped to capture smaller fish. Both species have long, tooth-filled jaws that swing wide open to grab and hold on to prey.