cintro.qxd 11/7/03 10:11 AM Page 9 • • • • Fish Anatomy ANATOMY (Body, Function, and Relation to Angling) Size Fish range widely in size. On the bantam side of the spectrum are tiny Philip- pine gobies less than half an inch long, the smallest of all animals with back- bones. 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 of more 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. 9 cintro.qxd 11/7/03 10:11 AM Page 10 Anatomy of a Perch Spiny dorsal fin Soft Body dorsal fin muscles Vertebrae Caudal Brain Lateral fin Skull line Eye Anal fin Tongue Gills Soft rays Heart Air Spiny rays Liver bladder Anus Stomach Gonad Spleen Pelvic Kidney Pyloric fin Intestine caeca 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. Anatomy of a Shark Second Spinal nerve cord Caudal fin dorsal fin First dorsal fin Vertebrae Muscle Brain Skin Kidney Gonad Eye Nostril Anal fin Gills Stomach Heart Mouth Clasper Pelvic fin Pancreas Liver (male) Spiral Gall Anus valve bladder Pectoral fin 10 Fish Anatomy cintro.qxd 11/7/03 10:11 AM Page 11 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. Form 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 unde- tectable as it lies flat on the sandy or muddy bottom, an adaptation that pro- tects 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 Fish Anatomy 11 cintro.qxd 11/7/03 10:11 AM Page 12 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 gener- ally 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. Scales 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 Fish Shapes Anatomical differences among fish are most obvious in general body shape but also include body and tail fins. 12 Fish Anatomy cintro.qxd 11/7/03 10:11 AM Page 13 growth slowing or stopping during winter when food is scarce and becom- ing much more rapid during the warm months when food is plentiful. Experts in reading scales can tell when a fish first spawned and each spawn- ing 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).