Among vertebrate animals, nowhere is the diversity of size and shape greater than in fish. The whale shark can be 50 feet long and a Sumatran carp is sexually mature at just 3/8 inch. There are fish that can soar, fish that can walk on land, and fish that climb the rocks of a vertical waterfall.
That astounding variation is even present among related species, and sunfish are a perfect example. Although the more than 20 species of sunfish all have a similar body shape and other characteristics, the slight differences in their mouth configurations alone represent huge differences in feeding behaviors.
Redbreasts, for example, are the most riverine of the group. As such, they have a mouth that is turned slightly downward because they have to endure faster currents than others while feeding. With its mouth pointed down, a redbreast can eat insect larvae and worms along the bottom without having to tip its tail-end upward into the current. The lesson: If you target redbreasts, you need to present your bait as close to the bottom as possible.
For bruiser 'gills, there isn't a whole lot they won't eat. Larger bluegills, however, have a mouth shape and musculature lets them suck in prey from a greater distance and while swimming faster. In fact, the greatest suction pressures recorded in bony fishes came from a 'gill. The message to anglers is simple: Once you've located some bulls, keep your offering on the move to exclude the smaller fish.
Pharyngeal jaws also play a role in feeding tendencies. Pumpkinseeds, redears and spotted sunfish all sport large sets of these secondary jaws in the throat, which help process prey, as well as swallow food. Spotted sunfish have the smallest of the three, although they can still crush thin-shelled snails, and their little pharyngeals allow for a mouth shape that creates enough suction to still inhale grass shrimp and insects.
Pumpkinseeds' pharyngeals are loaded with molar-like teeth that serve as anvils against which they pound snails and clams, and redears' are even bigger. However, these crushing jaws come at a cost. The larger muscles that power them make their heads thicker and meatier, which impair their ability to be suction feeders like bluegills, which have small pharyngeals that don¹t get in the way of the vacuum pump in their heads.
Use these characteristics to your advantage while targeting each sunfish variety. If, for example, you want to catch beefy redears, find a weedbed with lots of snails, and let a small crayfish, worm or a fat-body jig probe the weeds for you. But remember, since it takes shellcrackers longer to capture and eat your offering, let them munch for a second or two before you set the hook, then hold on.
Pharyngeal jaw size and configuration drastically affect a sunfish's feeding behavior. Seen here from left are the jaws of a 13-inch redear, 9-inch pumpkinseed, and a 10-inch bluegill. The larger pharyngeals of the redear and pumpkinseed are not only big, but also covered with teeth used to crush snails and clams. Their size, however, prevents 'seeds and shellcrackers from sucking in fast-moving prey as smaller-jawed bluegills can.