The beautiful coloration of fish can be appreciated only when observing them alive, for at death the brilliance and the intensity of color begin to fade immediately. Unquestionably, many fish equal or surpass in appearance the most spectacular colored bird or butterfly, and some of the blends and contrasts of body color are impossible to describe with justice.
The color in fish is primarily produced by skin pigments. Basic or background color is due to underlying tissues and body fluids. Iridescent colors are present in body scales, eyes, and abdominal linings of some fish. The rainbowlike reflecting hues of certain kinds of fish are caused by skin pigmentation fragmenting through the irregular ridges of transparent or translucent scales.
All fish are not highly colored, however; the range extends widely from fish with bright colors to species that are uniformly drab in brown, gray, and even pitch black. In nearly all species, the shades and the acuteness of color are adapted to the particular environment a fish inhabits.
In oceanic fish, basic color may be separated into three kinds: silvery in the upper-water zone, reddish in the middle depths, and violet or black in the great depths. Those that swim primarily in the upper layers of ocean water are typically dark blue or greenish blue on the dorsal portions, grading to silvery sides and white bellies. Fish that live on the bottom, especially those living close to rocks, reefs, and weedbeds, may be busily mottled or striped. The degree of color concentration also varies depending on the character of the fish's surroundings. For example, a striped bass caught from a sandy area will be lighter in general coloration than one captured from deeper water or from around dark rocks.
The same natural rules apply to freshwater fish. A northern pike, a pickerel, or a muskie is patterned in mottled greens because its habitat is primarily aquatic plants, where it is well camouflaged in alternating light and dark shadows. The bottom-dwelling, dark-backed catfish are almost impossible to detect against a muddy background.
Many anglers are bewildered by the color variances in trouts. Often the same species taken from different types of localities in the same stream may differ in coloration to a startling degree. For example, a trout taken from shallow, swiftly running water over sand and pebbles will be bright and silvery in comparison to a relative that lives under a log in a deep, quiet pool. The steelhead, a sea-run rainbow trout, is another good example of color change. When it leaves the ocean to enter western rivers, it is brilliantly silver, but as it remains in freshwater, the characteristic coloration of the rainbow trout develops: a dark greenish-blue back, a crimson lateral band, and profuse black spots over most of the body.
Regardless of the confusing differences under varying conditions, anglers who know the basic color patterns can easily identify any trout. Each species has recognizable characteristics that do not change. The brook trout, Salvelinus fontinalis, for example, always has reticulated or wormlike markings on its back, whereas the under edge of the tail fin and the forward edges of the pectoral, ventral, and anal fins are white.
Most types of fish change color during the spawning season; this is especially noticeable among the trout and the salmon tribes. As spawning time approaches, the general coloration becomes darker and more intense. Some examples are surprising, especially in salmon of the U.S. Northwest. All five species are silvery in the ocean, but as they travel upstream to their spawning grounds, they gradually alter to deep reds, browns, and greens—the final colors so drastically different that it seems hardly possible the fish were metallic bright only a short time earlier. Each type of salmon, however, retains its own color characteristics during the amazing transition.
In some types of fish, the coloration intensifies perceptibly when the fish is excited by prey or by predators. Dolphin (mahimahi), a blue-water angler's delight, appear to be almost completely vivid blue when seen from above in
a darting school in calm waters. When a dolphin is brought aboard, the unbelievably brilliant golden yellows, blues, and greens undulate and flow magically along the dolphin's body as it thrashes madly about. These changes in shade and degree of color also take place when the dolphin is in varying stages of excitement in the water.
A striped marlin or a blue marlin following a surface-trolled bait is a wondrous spectacle of color to observe. As it eyes its quarry from side to side and maneuvers into position to attack, the deep cobalt-blue dorsal fin and bronze-silver sides are at their zenith. This electrifying display of color is lost almost immediately when the fish is boated.
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