Feeding: biting, sucking,chewing, and swallowing - Fishes

Feeding: biting, sucking, chewing, and swallowing

Adaptations concerned with feeding clearly involve structures used in food acquisition and processing, such as jawbones and muscles, teeth, gill rakers, and the digestive system. Less obvious, but also important, are morphological adaptations in eye placement and function, body shape, locomotory patterns, pigmentation, and lures. The functional morphology of feeding deserves detailed exploration because of its intimate linkage to all aspects of fish evolution and biology.

For many fishes, a simple glance at jaw morphology, dentition type, and body shape allows accurate prediction of what a fish eats and how it catches its prey. Small fishes with fairly streamlined and compressed bodies, forked tails, limited dentition, and protractible mouths that form a circle when open are in all likelihood zooplanktivores. This generalization holds for fishes as diverse as osteoglossiform mooneyes, clupeomorph herrings, ostariophysineminnows, and representative acanthopterygian groupers(e.g., Anthias), snappers (Caesio), bonnet mouths (Inermia),damselfishes (Chromis), and wrasses (Clepticus). Large, elongate fishes with long jaws studded with sharp teeth for holding prey, and with broad tails adjoined by large dorsal and anal fins set far back on a round body are piscivoresthat ambush their prey from midwater with a sudden lunge. An alternative piscivorous morphology includes a more robust, deeper body, with fins distributed

around the body’s outline, and a large mouth with small teeth for short chases and engulfing prey; this is the “bass “morphology of many acanthopterygian predators such as kelp basses, Striped Bass, seabasses, black basses, and Peacock Bass, all in different families.

Generalized body shapes in predators do not exclude highly successful specialists that have arrived at very differentsolutions to catching mobile prey. Examples include lie-in-wait and luring predators (goosefishes, frogfishes, scorpionfishes, stone fishes, flatheads, death-feigning cichlids),cursorial predators that run down their prey (needlefishes, Bluefish, jacks, mackerels, billfishes), electro genicpredators that shock prey into immobility (torpedo rays, electric eels), or fishes with either an elongate anterior or posterior region for slashing and incapacitating prey(thresher sharks, sawfishes, billfishes).

A strong correspondence between morphology and predictable foraging habits exists in most other trophic categories, including herbivores (browsers, grazers, phytoplanktivores),scavengers, mobile invertebrate feeders, sessile invertebrate feeders, and nocturnal planktivores, to name a few. Convergent solutions to similar selection pressures are a striking characteristic of the foraging biology of fishes (Keast & Webb 1966; Webb 1982).

Our emphasis here will be on the functional morphology of structures directly responsible for engulfing and processing food. Moderate detail is provided, but we can only superficially discuss the diversity in structure, action, and inter connection among the 30 moving bony elements and more than 50 muscles that make up the head region of most fishes.