PUBLICATION 420-525 Sustaining America’s Aquatic Biodiversity Freshwater Fish Biodiversity and Conservation Louis A. Helfrich, Department of Fisheries and Wildlife Sciences, Virginia Tech Richard J. Neves, Department of Fisheries and Wildlife Sciences, Virginia Tech early 800 native fish species in 36 families Unfortunately, nongame fishes have declined sharply inhabit the freshwater rivers, streams, and in abundance and diversity in the last 20 years. Twen- lakes of the United States and Canada. North ty-seven species of fishes have become extinct during NAmerica has the most diverse temperate freshwater the past century. At least 16 species of fish have be- fish fauna in the world. Only about 5 percent of these come extinct in the United States since 1964. Nearly are the familiar sport or game fishes like trout and all of the fishes in the Colorado River are endangered bass. The remaining 95 percent are little known, but or threatened. Of the 490 Southeastern freshwater colorful, nongame (not sport fish) fishes such as dart- fishes, 91 are in trouble. At present, nearly 20 percent ers, minnows, shiners, and dace. of the native freshwater fishes in North America are imperiled, meaning that they are endangered, threat- About one-third of North American fishes are in the ened, or of special concern. minnow family (Cyprinidae), and about one-fifth are in the darter and perch family (Percidae). The East- What Is a Fish? ern United States has nearly four times as many fish species as the western states, yet the Southwestern Fish are cold-blooded animals with a backbone (ver- deserts have a remarkable fish fauna. The Southeast- tebrates), gills for breathing underwater, and paired ern United States harbors the greatest diversity of fins for swimming. They live underwater and are fish, with over 600 native fishes. States with the rich- dependent on water for dissolved oxygen, support, est diversity of fish include Tennessee (307 species), food, and shelter. Marine mammals (whales, dol- Kentucky (242 species), and Virginia (217 species). phins, seals, sea otters), reptiles (turtles), amphibians (frogs and salamanders), shellfish (oysters, clams, and Nongame fishes, although not pursued by anglers, are mussels), and aquatic invertebrates (crayfish, starfish, nevertheless important. They serve us in many ways lobster) are not fish. Although they may not look like and deserve our protection. Nongame fishes are an fish, seahorses and eels actually are fish. important ecological link in the food chain, feeding on insects and serving as prey for sport fishes, birds, The three main groups of fish are and other wildlife. They also are important indicators • jawless fish (lampreys), of water quality and ecosystem health. For example, a • cartilaginous fishes (sharks and rays), and fish kill or the disappearance of fishes from a stream • bony fishes (most fish species). can alert citizens to water pollution. www.ext.vt.edu Produced by Communications and Marketing, College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University, 2009 Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Rick D. Rudd, Interim Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Alma C. Hobbs, Administrator, 1890 Extension Program, Virginia State, Petersburg. The first two groups are primitive, ancient fishes, where- How do fishes breathe? All animals need oxygen to as the bony fishes are more recent, advanced fishes. survive. Land animals breathe atmospheric air that contains 21 percent oxygen. However, oxygen is not Fish exhibit the greatest biodiversity of the vertebrates always available in water. Dissolved oxygen levels in (animals with backbones) with over 22,000 species. water can range from 0 percent to over 100 percent Of these, about 58 percent are marine, 41 percent are saturation, depending on water temperature, eleva- freshwater species, and 1 percent move back and forth tion, air pressure, other dissolved gases, and water between salt- and freshwater. As expected, marine quality. fishes are the most diverse because saltwater covers 70 percent of the earth. Only 1 percent of the earth is Fish extract dissolved oxygen from the water using covered by freshwater. their gills. In breathing, This small area is home to Dorsal Fin fish first gulp a mouthful 8,000 species of freshwater of water, then close their fishes. Gil Plate Adipose Fin mouths, and pressurize Eye Caudal Fin the water, forcing it over Anglers prefer sport fish Jaws the rich red blood supply (trout, bass, and pike) Lateral Line of gills and out the oper- for their fighting or food cula (gill-flaps). Oxygen value. In contrast, non- is absorbed directly into Anal Fin game fish are not com- Barbels Throat the fish’s blood supply Pelvic Fin monly sought by anglers Pectoral Fin and distributed through- because they are small fish out the body via the (minnows, darters, and Figure 1. External featues of a Composite fish circulatory system. dace) or not particularly good eating (carp, goldfish, bullheads, lamprey, and Some fishes have an internal, inflatable air (swim) gar). Ninety-five percent of fish are nongame fish. For bladder that evolved as an outgrowth of the intestine. example, of the 217 species of fish found in Virginia, The air bladder can be inflated or deflated to regulate only 25 are considered game fish. buoyancy and depth. Some fish use their air bladders to amplify underwater sound, and thereby increase their The science and study of fish is called ichthyology ability to hear. Gar and lungfishes use their air blad- (from the Greek word for fish, ichthyes). Fish have ders to gulp and breathe atmospheric oxygen. They can been raised and studied for centuries, beginning with survive in low-oxygen water for long periods. the early Chinese, Egyptians, and Greeks. The farming of fish and other aquatic animals is called aquaculture. Nearly all fish have a protective slimy mucus cover- ing their skin. This outer coating reduces friction and Structure and appearance increases swimming speed. It also protects fish from parasites and diseases, and permits salt balance (os- Fish exhibit a variety of body forms. Some are moregulation). Removing the mucus layer by netting streamlined, torpedo-shaped (trout, sharks, and sail- and handling fish can increase their susceptibility to fish), allowing them to slip easily through the water. disease and disrupt their salt balance. Others are flattened top to bottom (flatfish and rays) for living on the bottom and making surprise attacks Many fish are armored with transparent plates called on prey. Some fish are flattened laterally (sunfishes) scales that overlap like roof shingles. Some fish have so they can make quick turns. Long, thin, needle- no scales. Others have scales that reflect silvery light shaped fish (gar and pike) are designed for high to confuse predators. Scales are used to identify fish forward speed to catch prey. Pipefish and angelfish species and to age fish. By counting the number of mimic the leaves of waterweeds for camouflage. scales along the lateral line (mid-body hearing organ), Fish vary in size more than any other group of ver- ichthyologists can accurately identify each fish spe- tebrates. The world’s biggest fish is the whale shark cies. Under the microscope, growth rings on scales which reaches 50 feet in length and weighs over 20 can be counted like tree rings to determine the age of tons. The smallest fish is the pygmy goby, which a fish. reaches only 0.3 inch in length. 2 Fish use their fins to stop, start, steer, turn, swim Salmon, American eels, and a few other fish can backward and forward, chase and catch food, and migrate between fresh- and saltwater. Salmon are migrate. The large, powerful tail (caudal) fin is impor- anadromous fish that are born in freshwater, migrate tant for forward speed. All fins, including the dorsal to and live in the ocean, and then return to freshwater (top), pectoral (chest), and pelvic (abdominal) fins, (often their birth stream) to reproduce (spawn) and are used in swimming and maneuvering. The dorsal, die. Eels are catadromous fish. They are born in the caudal, and anal fins are median, unpaired fins. The ocean and migrate to freshwater to live, only return- pelvic and pectoral fins are paired. ing to the ocean to spawn. Fin shape and location are important for swimming The rich diversity of fish (25,000 species) is due to and maneuvering. Fast swimming fish (tuna and the diversity of aquatic habitats and the range of wa- swordfish) have long pointed and crescent-shaped fins ter quality in which they can live. It also results from that fold into body slots to reduce drag. Flying fish immense isolation in time and space (fish evolved have long, broad wing-shaped fins that allow them to over millions of years in oceans worldwide). jump and glide long distances above the surface. Puffer and box fish have small, rapidly-beat- Fish diversity is greater in streams than in lakes. ing fins for fine maneuvering. Frequently two to ten species of fish can be found in small streams, 15 to 30 species in an intermediate- Fins contain supporting sized stream, and 20 fin rays that can be soft, to 40 fish species in a hard, or a combination of river. An exceptional both. Hard, sharp fins can diversity of fishes is deliver a painful (even found in the South- toxic) jab when erected eastern United States, (some catfish). Pectoral where as many as 90 fins can be large and species of fish may live broad as in flying fishes in a single river.