Teeth Food and Digestion

A tremendous diversity exists in the form and the size of fish teeth. The character of the dentition is a clue to the fish's feeding habits and the kind of food it consumes. Of all the fish, some sharks display the most awesome arrays of teeth: profuse and well structured for grasping, tearing, and cutting. The barracuda's teeth are different from any shark's, but they also draw attention because of their ferocious appearance. They are flat, triangular, closely set, and extremely sharp. Such teeth are ideally adapted for capturing live fish, the barracuda's main diet. Small victims are usually swallowed whole; the

Superficial I

Broad striated muscles make up the bulk of the body of a fish; they run in irregular vertical bands and various patterns, and are functional in swimming.

Superficial I

Broad striated muscles make up the bulk of the body of a fish; they run in irregular vertical bands and various patterns, and are functional in swimming.

segments

Cheek i muscles Muscle segments larger ones may be cut in two and each piece swallowed separately. The bluefish, well known for its ability to chop up a school of baitfish, has teeth of a similar nature but smaller in size.

Some fish possess sharp, conical teeth (called canine, or dog, teeth); pike, pickerel, and muskies are good examples. Such teeth cannot cut but do a good job of grasping and piercing. Fish fortified with canine teeth generally hold a baitfish until its struggles diminish before swallowing it—a fact taken into consideration by anglers before setting the hook. Anglers must exercise extreme caution when removing hooks from sharks, bluefish, barracuda, pikelike fish, and other fish with dangerous dentition.

The yellow perch, the sea bass, the catfish, and other species have multiple rows of numerous short and closely packed teeth that resemble the tips of a stiff brush. Such an arrangement meets the fish's need to grasp a variety of food off the bottom or hold prey in a sandpaperlike grip until ready to be eaten.

Some kinds of fish have sharp-edged cutting teeth called incisors, located in the forward part of the mouth; some are saw-edged, others resemble human teeth, and still others are variously fused into parrotlike beaks. Par-rotfish, for example, have such teeth and thrive on small organisms nibbled from corals, rocks, and reefs. Some bottom-dwelling fish, such as skates, rays, and drum, have molarlike teeth that are well adapted for crunching crustaceans, mollusks, and other organisms.

Many fish, including some of the more common types such as carp, minnows, and suckers, have teeth in their throats. These pharyngeal teeth are sharp in some species, molariform in others, and only remnants in still others. There are fish that have teeth on the roof of the mouth (vomerine and palatine) and on the tongue. Pike, pickerel, and muskies, for example, have vomerine teeth that are profuse and closely packed, whereas other fish, such as certain trout, have comparatively few teeth on these areas. One of the distinguishing features between a true trout and a charr (rainbow trout versus brook trout, for example) is the presence or absence of vomerine teeth. The vomerine bone in the center of the charr's mouth has only a few teeth, located on its forward end, whereas the vomer of a true trout is much longer and has teeth all along it. Some fish have teeth on the very edges of their mouths (premaxillary, maxillary, or both). And many planktonic feeders, such as the menhaden, have no teeth at all; instead, their long gill rakers help in retaining the microscopic organisms they take into their mouths.

Fish are a tremendously diversified group of animals, which feed on an extensive variety of foods. Some, when mature, feed exclusively on other fish; others feed entirely on plants. The sea lamprey, a parasitic, highly unattractive eel-like fish, uses its funnel-shaped mouth, lined with radiating rows of sharp teeth, to attach itself to the body of a live fish; then, using its toothed tongue, it rasps a hole in its prey and sucks out blood and body fluids.

In general, the food plan of a fish's life is to eat and to be eaten. Such a scheme involves a food chain. Nutrients in the water nourish various types of free-flowing aquatic plants (phytoplankton) that are eaten by a variety of microscopic animals (zooplankton). A tiny fish feeds on zooplankton, and the bigger fish feeds on the smaller fish. There are many steps in this food chain, as larger fish eat smaller ones until the chain may end with, for example, a bluefin tuna. The tuna eventually expires and sinks to the bottom, where it is eaten by worms, crabs, and other bottom dwellers. Finally, bacteria return the nutrients to the water in a soluble inorganic form, which the phytoplankton again utilize. The food chain is then complete.

Insects, worms, snails, mussels, squid, and crabs are some of the important larger invertebrates that provide food for fish. Amphibians, reptiles, birds, and mammals, as well as other fish, are also included in the diet of fish. Largemouth bass and muskies, for example, commonly eat frogs and occasionally small turtles or snakes. Gar have been caught that contained bird remains in their stomachs. And goosefish—bottom dwellers with huge mouths—will capture such unusual prey as a diving duck.

Fish also differ in the way they feed. Predators entrap or cut their prey by using their well-developed teeth. Grazers or browsers feed on the bottom. Fish that feed on tiny organisms sifted from the water by using their long gill rakers are known as strainers. Suckers and sturgeon have fleshy, distensible lips, well suited to suck food off the bottom, and thus are suckers. Some lampreys depend on the blood and the fluids of other fish to live; they are categorized as parasites.

Here are a few examples of the structural adaptations of fish that assist them in feeding: catfish and sturgeon have whiskerlike feelers for touching and tasting food before accepting it; sailfish, marlin, and swordfish may stun their prey with their clublike bills before devouring it. The paddlefish employs its long, sensitive, paddlelike snout to stir up the bottom organisms on which it feeds. Gar have elongated snouts filled with needlelike teeth that make formidable traps for capturing prey. The goosefish, also known as the angler, has a long, slim appendage with a piece of skin at its tip, located on the forward part of its upper snout; this appendage can be wiggled like a worm and acts as a lure to entice prey.

Generally, fish that live in a temperate zone, where seasons are well defined, will eat much more during the warm months than they will during the cold months. In this zone a fish's metabolism slows down greatly during winter. The body temperature of most fish changes with the surrounding environment; it is not constant, as it is in mammals and birds.

The digestive system of fish, as in all other vertebrates, dissolves food, thereby facilitating absorption or assimilation. This system, or metabolic process, is capable of removing some of the toxic properties that may be present in foods on which fish feed.

The basic plan of the digestive tract in a typical fish differs in some respects from that of other vertebrate animals. The tongue cannot move as it does in higher vertebrates, and it does not possess striated muscles. The esophagus, or gullet (between the throat and stomach), is highly distensible and usually can accept any type or size food that the fish can fit into its mouth. Although choking does happen and has been particularly noticed in pickerel and pike, a fish rarely chokes to death because of food taken into its mouth.

Fish stomachs differ in shape from group to group. The predators have elongated stomachs. Those that are omnivorous generally have saclike stomachs. Sturgeon, gizzard shad, and mullet, among others, have stomachs with heavily muscled walls used for grinding food, just as the gizzard of a chicken does. Some of the bizarre deep-sea fish possess stomachs capable of huge distention, thereby enabling them to hold relatively huge prey. On the other hand, some fish have no stomachs; instead, they have accessory adaptations, such as grinding teeth, that crush the food finely so that it is easily absorbed.

Intestinal structure also differs in fish. The predators have shortened intestines; meaty foods are more easily digested than are plant foods. In contrast, herbivores, or plant eaters, have long intestines, sometimes consisting of many folds. Sharks and a few other fish have intestines that incorporate a spiral or coiled valve that aids in digestion. Lampreys and hagfish have no jaws and do not have well-defined stomachs or curvature of the intestines. Lampreys need a simple digestive system because they are parasites that subsist on the blood and juices they suck from other fish. During the long migration from the sea upriver to spawn, the various species of salmon never feed. Their digestive tracts shrink amazingly, allowing the reproductive organs to fill up their abdomens.

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