Shared Characteristics—What Makes A Fish A Fish?

While fish share many of the same basic organs as you and I, they do have some unique attributes.

Cold-Blooded—To begin, fish don’t maintain a higher body temperature than their surroundings, as do mammals. Instead, their bodies are the same temperature as the surrounding water—warm in summer, cold in winter. This often leads to increased activity and heavy feeding in summer, and lethargic behavior in winter, but once again, it depends on the individual species. Some species remain quite active in winter, providing good ice-fishing opportunities.

Temperature Preference—This can be a somewhat misleading topic, because most fish can tolerate a wide range of water temperatures. Still, each species tends to function best within a certain broad band of temperature. Certain species must avoid excessively warm or cold temperatures in order to survive. You don’t, for example, find bass in the icy waters of northern Canada, nor lake trout in the warm waters of the southern U. S.

Gills—Passing water over the gills reoxygenates blood flowing through the gill filaments. Fish expel water through the backs of their gill openings even at rest, so they don’t have to be swimming in order to breathe. Never touch a fish’s gills; they’re prone to injury.

Swim Bladder—This interesting organ functions much like a balloon, allowing fish to either retain or dissipate sufficient air to maintain buoyancy when they change depth levels and experience different water pressure against their bodies. Most freshwater fish are limited to doing this rather slowly over an extended period, although some can expel air rather quickly when they move rapidly to the surface, as the air within their swim bladder expands due to reduced pressure. While most species can make significant but brief depth changes to feed on an easy meal, they tend to return rather quickly to their original depth to equalize pressure. This may explain why fish tend to remain at or near specific depth levels with comfortable surroundings.

Fins Galore—Look at any fish, or accurate artwork depicting a fish, and you’ll probably be surprised at how many different fins they have. All serve a function, chiefly for steering and maneuvering, like a combination of adjustable flaps on an airplane and thruster rockets on a spaceship. Their main propulsion, meanwhile, comes from sequentially coiling and uncoiling their bodies and caudal fin (commonly known as a tail fin) to each side.

Body Shape—Long, slender fish like pike and muskies are typically known for bursts of speed, but tend to be less maneuverable in and around cover. Shorter, flatter fish like panfish (bluegills, crappies) are better able to weave through cover and obstructions, but lack the long body to propel themselves at high speeds. Intermediate body shapes, like those of bass and walleyes, tend to fall in between. Trout, salmon and stripers tend to be the fastest freshwater species, largely due to their body shape and muscular nature.

Physical Size—With freshwater species ranging from half-pound sunfish to 500-pound sturgeon, there’s plenty of variation. While each species grows to a typical size range, most freshwater fish are less than ten pounds, with the vast majority under thirty. Two prominent exceptions are stripers and salmon, which have their roots in saltwater.  Big catfish, alligator gar and the aforementioned sturgeon can reach and surpass 100 pounds.

Mouth Size And Shape—You might not think this is a big deal, but it is. After all, fish can only eat what will pass through their mouths. Fish with large mouths tend to prefer large meals (usually comprised of smaller fish), while smaller fish like panfish are limited to eating insects or small minnows, chiefly because that’s all that fits between their gums. Most fish, however, tend to feed by inhaling a vortex of water along with their prey, expelling the water through the gills, and trapping the prey in their mouths. They don’t simply swim up to and bite something with their jaws.

Teeth—Toothy critters like pike and musky tend to be ferocious predators, and can easily cut your line if you don’t use a wire leader to deflect their rows of sharp teeth. Yet some fish, like walleyes and sauger, have rounded teeth that won’tyou’re your fishing line; the line rests between their teeth, rather than being sawed and severed. Other fish, like panfish, bass and catfish, have roughened surfaces along their gums, rather than teeth, yet still function as efficient predators. Big cats have powerful crushing jaws, however, so be careful where you put your hand. In all cases, keep your fingers out of mouths with teeth.

Oxygen—All fish need to extract oxygen from the water, but some species require higher oxygen levels to survive. Most unpolluted waters provide adequate oxygen content above five parts per million throughout the year, although in some cases, the deepest portion of a lake may suffer oxygen depletion during the extreme heat of summer, or beneath the ice during a severe winter. If so, some species are unable to survive until the water is reoxygenated by natural causes. Carp, catfish and some warmwater species appear best at withstanding poor oxygen levels, while coldwater fish are usually the first to perish when stressed.