Based on feeding habits, researchers broadly classify ray-finned fishes as herbivores, carnivores, omnivores, zooplanktivores and detrivores. There is considerable nuance within each of these categories because many fish are opportunistic feeders – they tend to consume whatever is around, especially when food is scarce. However, primary feeding habits are often associated with body form, mouth type and digestive apparatus, as well as teeth. For instance, gars , pike-characids , pike , needlefish , pike killifish and barracuda represent a diverse range of taxa, yet they all have elongate (long and narrow) bodies, long snouts, and sharp teeth with the fins placed toward the back of the body; this is the design of a fast-start predator, which often lurks motionless in the water column, slightly camouflaged and ready to lunge quickly at unsuspecting prey. These fishes are not made for sustained speed and maneuverability, whereas tunas and billfishes (suborder Scombroidei), with their rounded and highly tapered bodies, are streamlined pelagic chasers capable of very high speeds over long periods. These two fishes are termed ram feeders. Other predators avoid the extra energy expenditure of chasing prey, and instead wait passively, depending largely on good vision, explosive thrust and large mouths capable of forming strong vacuums and effectively inhaling prey (the latter method is termed suction feeding). These sit-in-wait predators are often completely hidden with elaborate camouflage or by burying themselves beneath sediment with only the eyes exposed. Fishes of this type include many scorpionfishes , flatheads , hawkfishes , sea basses , stonefishes , stargazers, flatfishes , frogfishes, and lizardfishes.
Herbivorous fishes posses specialized organs, such as extended guts, pharyngeal mills and gizzards, that allow them to exploit various reef plants and algae. Some of the most successful freshwater families (e.g. minnows , catfishes , cichlids), and most abundant coral reef families (e.g. halfbeaks , parrotfishes , blennies , surgeonfishes , rabbitfishes), include many species of herbivorous fishes. Several groups of herbivorous coral reef species defend territories or form feeding shoals (freshwater cichlids have many of the same behaviors). Some parrotfishes and surgeonfishes utilize shoals to overwhelm the defenses of territorial species, thus gaining access to areas with higher concentrations of plant material.
Zooplanktivores, which feed on small crustaceans like water fleas and copepods floating in the water column (termed zooplankton), abound in oceans throughout the world. Groups such as silversides , herrings and anchovies often congregate in feeding shoals numbering in the millions. Smaller shoals of zooplanktivores, such as rabbitfishes and the juvenile forms of many other reef species, are also found hovering above and around coral reefs. The characteristic features of zooplanktivorous fishes are small size, streamlined and compressed bodies, forked tails, few teeth, and a protrusible mouth that forms a circle when open. When patches of zooplankton are particularly high, many pelagic zooplanktivores keep their mouths agape, and when patches are low they pick animals out individually (the latter are also termed suction feeders).
As discussed in Communication, several groups of ray-finned fishes have quite peculiar methods of capturing prey. Deepsea anglerfishes , among many others in the Stomiiformes and Lophiiformes orders, have developed a luminous bait to attract prey in the deep, dark waters they inhabit. Turbid habitats are home to many fishes that utilize electroreception to find prey, and some predators (e.g. knifefishes and the electric eel) use intense electrical shocks of as much as 350 volts to stun prey before consuming them. Archerfishes exploit a food source that is unavailable to most other fishes: terrestrial insects in overlying vegetation. By shooting jets or bullets of water, and correcting for light refraction, archerfishes knock insects down to the water surface and quickly consume them. Finally, some boxfishes and triggerfishes use an equally novel technique for capturing prey. Both groups expel jets of water from their mouths to uncover buried animals, while triggerfishes use jets and their snouts to flip over and consume otherwise inedible prey, such as spiny sea urchins.
Foraging Behavior: stores or caches food ; filter-feeding
Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore , Eats eggs, Sanguivore , Eats body fluids, Insectivore , Eats non-insect arthropods, Molluscivore , Scavenger ); herbivore (Frugivore , Granivore ); omnivore ; planktivore ; detritivore
- Ferraris, C. 1998. Catfishes and Knifefishes. Pp. 106-112 in J Paxton, W Eschmeyer, eds. Encyclopedia of Fishes. San Diego, CA: Academic Press.
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