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ANATOMY (Body, Function, and Relation to Angling)
Fish range widely in size. On the bantam side of the spectrum are tiny Philippine gobies less than half an inch long, the smallest of all animals with backbones. They are so diminutive that it takes literally thousands of them to weigh a pound, yet they are harvested commercially for use in many foods. At the behemoth end of the spectrum are giant whale sharks 65 to 70 feet long. The largest whale sharks can weigh as much as 25 tons, but they are so docile, they may allow inquisitive scientists to pull alongside them with boats and then climb aboard to prod and poke as they give the big plankton-eaters a close examination. Between these extremes are seemingly limitless shapes and sizes among an estimated 21,000 species. This number exceeds the combined numbers of species of all other vertebrate animals-amphibians, reptiles, birds, and mammals.
Another giant of the sea is the mola, or ocean sunfish, which also goes by the name of headfish because its fins are set far to the rear on its broad, almost tailless body. Molas, which have the unusual habit of basking at the surface, lying on their side as though dead, may weigh nearly a ton but are not quarry for anglers. Also in saltwater, such highly prized game species as bluefin tuna, swordfish, and certain sharks and marlin reach weights ofmore than a thousand pounds, with some shark and marlin specimens weighing considerably more.
The white sturgeon, one of the largest of freshwater fish, formerly reached weights of well over a thousand pounds in the Columbia and Fraser Rivers but is now uncommon over 400 pounds. In the 1800s, monstrous sturgeon of over 2,000 pounds were reported, but fishery workers have not verified such legends. The prehistoric-looking alligator gar of the southeastern United States can attain a weight of 300 pounds.
Fish size is of special interest to anglers. Many anglers aspire to match their skills against the larger specimens of various game species; competitive events often place a premium on large individual catches; and other rewards, both materialistic and intangible, accrue to those who have caught fish deemed to be of large, if not trophy, caliber.
Records for freshwater and saltwater fish caught on rod and reel are maintained by the International Game Fish Association, based upon specific standards and on weight. Yet in many cases, fish are known to grow much larger than sport-caught records indicate. Two all-tackle record tarpon taken on rod and reel, for example, each weighed 283 pounds, which is admittedly sizable but much smaller than the 350-pounders that have reportedly been caught in nets. On the other hand, record rod-and-reel catches greatly exceed the average size of most species. Most brook trout taken by anglers, for example, weigh less than half a pound, but the sport-caught record for the species is 14 pounds, 8 ounces.
A fish does not have to be gigantic to provide fun, however. In this regard, tackle plays an important role. Anglers, using ultralight tackle in ponds and lakes, find it challenging to catch quarter-pound bluegills, rarely if ever hooking one that approaches a pound in weight, let alone the species' top record of 4 pounds, 12 ounces. Indeed, line-class record categories were long ago established for each species to recognize the angler's fishing skill by virtue of a notable catch for a particular weight of tackle.
Size is a relative issue, both in terms of a fish's fighting ability and in its desirability as a catch. Although most larger fish are more difficult to subdue than smaller ones, that is not always the case. Size is also not necessarily comparable between different species; a 10-pound steelhead, for example, provides far better sport than a 10-pound walleye, and a 10-pound bonefish is much more challenging than a 10-pound barracuda. Growing season and geographic location may be factors as well. A 10-pound largemouth bass in Florida, where a favorable growing season can allow a bass to grow large quickly, is akin to perhaps a 6-pound largemouth bass in Minnesota in terms of age and availability within the bass population, the result being that they are catches of similar accomplishment, despite being of different size.
The typical fish, such as the yellow perch, the largemouth bass, the striped bass, and the grouper, has a compressed body that is flattened from side to side. In others, the body is depressed from top to bottom, as in flounder, rays, and other bottom-hugging types. Still others are spindle-shaped or streamlined, like mackerel, tuna, and trout; and some, such as eels, have an elongated or snakelike body. All fish fit into one of these four categories, but each form in turn may differ with various adaptations in certain portions of its anatomy.
These differences fit the fish for specific environments or particular ways of life. For example, the streamlined tuna is an open-ocean fish that moves constantly, indulges in long migrations, and pursues fast-swimming schools of smaller fish. Its bullet-shaped body is well adapted for such a life. On the other hand, the flounder's depressed body allows it to be completely undetectable as it lies flat on the sandy or muddy bottom, an adaptation that protects it from enemies, as well as allows it to grasp unsuspecting prey. Marlin, sailfish, and swordfish are large fish with long snouts (bills) used as clubs to stun prey or as swords in defense. Eels and cutlassfish have slim, snakelike bodies, enabling them to negotiate seemingly inaccessible areas to hunt for food or to escape enemies.
Among the most unusual fish in shape are those that live in the deep sea. Many have luminous spots or stripes along their bodies, and fins may be reduced to slim filaments, some bearing bulbous and luminous tips. Many have long barbels around their mouths, with lighted tips that serve as lures for attracting smaller prey within reach of their strong jaws. In some, the tails are long and snakelike. Most have very large mouths and an array of long, dagger-sharp teeth that help in holding their catches. The mouth is generally stretchable, as is the stomach. When the fish has the good fortune to capture a meal in the dark depths, where food, as a rule, is scarce, it attempts to devour the prey regardless of size. These deep-sea fish are seldom among the species caught by anglers.
A typical fish's body is covered with thin scales that overlap each other like the shingles of a roof. They are prominent outgrowths of skin, or epidermis, in which numerous glands secrete a protective coating of slime, often referred to as mucus. The slime is a barrier to the entry of parasites, fungi, and disease organisms that might infest the fish, and it seals in the fish's body fluids so that they are not diluted by the watery surroundings. The slime also reduces friction so that the fish slides through the water with a minimum of resistance; it also makes the fish slippery when predators, including the human variety, try to grab hold. Some fish, such as lampreys and hagfish, give off copious amounts of slime.
As a fish grows, its scales increase in size but not in number. Lost scales may be replaced, however. The ridges and spaces on some types of scales become records of age and growth rate. These can be read or counted like the annual rings in the trunk of a tree to determine a fish's age-the fish's growth slowing or stopping during winter when food is scarce and becoming much more rapid during the warm months when food is plentiful. Experts in reading scales can tell when a fish first spawned and each spawning period thereafter. They can determine times of migration, periods of food scarcity, illness, and similar facts about the fish's life. The number of scales in a row along the lateral line can be used to identify closely related species, particularly the young. Growth rings occur also in the vertebrae and in other bones of the body, but to study these requires killing the fish. A few scales can be removed without harm to the fish.
Most bony fish have tough, shinglelike scales with a comblike or serrated edge (ctenoid) along their rear margins or with smooth rear margins (cycloid). The scales of garfish are hard and almost bony, fitting one against the other like the bricks on a wall. These are called ganoid scales. Sturgeon also have ganoid scales, some of which form ridges of armor along portions of their sides and backs.
Sharks have placoid scales, which are the most primitive type. These scales are toothlike, each with a central spine coated on the outside with enamel and with an intermediate layer of dentine over a central pulp cavity. The skin of sharks, with the scales still attached, is the shagreen of commerce, widely used in the past and still used today in primitive areas as an abrasive, like sandpaper, or to make nonslip handles for knives and tools.
The scales may be variously modified on different species. Some fish do not have scales at all. Most species of catfish, for example, are "naked" or smooth-skinned. Their skin is very slippery, however, and some of the rays in their fins are modified as sharp spines. Paddlefish and sculpin have only a few scales. The scales of mackerel are minute. Trout also have tiny scales. Those of eels are widely separated and buried deep in the skin.
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.
Fins and Locomotion
Fish are propelled through the water by fins, body movement, or both. In general, the main moving force is the caudal fin, or tail, and the area immediately adjacent to it, known as the caudal peduncle. In swimming, the fins are put into action by muscles attached to the base of the fin spines and rays. Fish with a fairly rigid body, such as the tilefish, the trunkfish, the triggerfish, the manta, and skates, depend mostly on fin action for propulsion. Eels, in contrast, rely on extreme, serpentlike body undulations to swim, with fin movement assisting to a minor extent.
Excerpted from Ken Schultz's Field Guide to Freshwater Fish by Ken Schultz Excerpted by permission.
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