A large member of the minnow family and an aquaculture species of worldwide importance, the grass carp is used for weed control because of its aggressive and herbivorous feeding habits. In the United States, where it was introduced in the early 1960s, it has become an extremely controversial species because of the biological damage it inflicts in the process of eliminating vegetation. This species is called the grass carp by critics, whereas supporters often refer to it as the white amur to avoid the negative connotations associated in North America with the name "carp."
Identification. The grass carp has an elongate and fairly compressed body, a wide and blunt head, a very short snout without the barbels found on common carp, a short dorsal fin, and a moderately forked tail. The terminal and nonprotractile mouth has thin lips and sharp pharyngeal (throat) teeth especially suited to its feeding habits. The grass carp is covered with large scales; the ones on the upper sides of the body have a dark border and a black spot at the base and give the fish a cross-hatched appearance. It is colored gray or green on the back, shading to white or yellow on the belly, and has clear to dark fins.
Size/Age. The grass carp grows quickly and to large sizes; some have been reported at 100 pounds in native waters. It can add 3 to 5 pounds a year to its weight under favorable conditions. The largest fish taken by rod and reel was a 68-pound, 12-ounce Arkansas specimen.
Life history/Behavior. Spawning takes place once a year over gravel bottoms in rivers, between April and September, according to temperature; adults will migrate upstream to find acceptable spawning sites. The round eggs of the grass carp are semibuoyant and amber colored, hatching in 24 to 30 hours without the protection of the parents. After they absorb the nutrients in their yolk sacs in the first 2 to 4 days
white amur, amur, carp; French: carpe amour, carpe herbivore, amour blanc; German: graskarpfen; Japanese: sogyo.
Distribution. Found originally in China and eastern Siberia, specifically in the Amur River basin from which it gets its name, the grass carp has been widely introduced to more than 20 countries. Only those in certain areas have been able or allowed to reproduce naturally; these places include the Danube River in central Europe, the Mississippi River in North America, and Russia and southern Africa. In the United States, the grass carp was first stocked in Arkansas waters in 1963 and intentionally released in 35 states, although it has subsequently spread to other bodies of water where it was unwanted. In fact, many states have made it illegal to stock grass carp within their borders, unless a permit issued by the appropriate fisheries management agency has been obtained.
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Carp, Crass (continued) Habitat. Occurring in freshwater, grass carp inhabit lakes, ponds, pools, and backwaters of large rivers, with a preference for slow-flowing or standing bodies of water with vegetation. They are able to withstand temperature variation, extreme salinity, and low oxygen concentrations.
of their lives, the larvae feed on microplankton in quiet waters. The young hide in deep holes in riverbeds during the winter.
Food and feeding habits. Primarily vegetarians, grass carp have earned their name by eating aquatic plants and submerged grasses, adding the occasional insect or invertebrate. With the help of teeth on the pharynx, they tear off vegetation with jerking motions. Unlike common carp (see: Carp, Common), grass carp do not muddy the water with their browsing, but their aggressive feeding habits cause other problems. Grass carp tend to break off the upper portions of grasses, leaving the roots to grow, so they are not as useful in eradicating vegetation as they are supposed to be. Also, grass carp cannot digest all the plant matter they take in, so instead of eliminating a vegetation problem, they make it worse by excreting plant material and distributing it to new areas. In addition, they contribute to increased water turbidity and to eutrophication. Finally, heavy browsing may stimulate faster than normal growth in certain kinds of plants.
Triploid grass carp. A technique that consists of exposing fertilized eggs to heat shock was invented by researchers in 1981 to produce sterile grass carp. This method creates nonreproducing fish of both genders. They are called triploid grass carp because they have three sets of chromosomes, instead of the usual two sets (those fish are called diploid). They are as hardy as the ordinary variety of grass carp, but they have the benefit of not being able to over-populate their habitats. They look like large creek chub, flourish in warm water, and may reach weights of 25 pounds or more. Triploid grass carp are useful in controlling unwanted aquatic plants, but the water clarity may deteriorate due to the substantial passing of plant material as fecal matter.
Catfish comprise a large group of predominately freshwater fish that is distributed around the world. Some accounts peg the total number of catfish species worldwide at more than 2,200. Many of the world's significant river systems are home to at least one species of catfish, and in most cases these fish rank among the largest fish of the river system. The same applies to large lakes, especially in reservoirs that are impoundments of large rivers. Many catfish are important for commercial and recreational purposes.
Species. Most catfish are scaleless, but some are armored with heavy scales. They vary in size from tiny versions that are popular for aquarium use, the smallest of which grow no larger than V2 inch, to huge specimens, the largest of which has been recorded at more than 600 pounds. Most catfish prefer the sluggish localities of lakes and rivers; some do best in fairly swift waters. Tenacious fish, they can stay alive out of water for a considerable time, especially if kept moist. They are characterized by having a single dorsal fin and an adipose fin; strong, sharply pointed spines in the dorsal and pectoral fins; and whiskerlike sensory barbels on the upper and lower jaws. The head and the mouth are generally broad, and the eyes small.
North American freshwater catfish. Members of the family Ictaluridae, North American freshwater catfish are distributed from Canada to Guatemala and contain about 50 species. These bottom-loving fish are important commercially, and many millions are harvested annually, some from natural environments and some from aquaculture or fish-farming operations.
Thousands of anglers pursue these fish, employing a wide variety of methods to catch them. All species obtained from fairly clear waters are delicious on the table. Many fish farms specialize in raising and marketing catfish. All
members of this group have scaleless skins and a stiff, sharp spine at the leading edge of the dorsal fin and pectoral fins. Just in front of the tail, on the dorsal surface, is a fleshy adipose fin. Its eight barbels are sensory structures that help the catfish to locate food.
Nearly all North American catfish live in sluggish streams or in the quiet waters of lakes and ponds. They are bottom feeders, taking both live and dead foods. They are typically active at night—although some are more active than others during the day—and on dark, overcast days or in roiled, murky water. Catfish spawn in the spring and the early summer, fanning nest areas in the sand or the mud. One or both parents stand guard until the eggs hatch and then shepherd the young until they are large enough to fend for themselves.
Perhaps the most abundant and best-known members of the clan of about a dozen species of the genus Ictalurus are the three principal species of bullhead: brown bullhead, black bullhead, and yellow bullhead.
Also of commercial and recreational importance in some areas are channel catfish, blue catfish, white catfish, and flathead catfish. The largest is the blue catfish, which may tip the scales at more than 150 pounds.
The foregoing North American catfish are not finicky about what they eat. They will accept almost anything offered for bait, although some are more finicky than others, and this is not to imply that they will strike anything at any time, only that they have eclectic tastes. Biologists have found strange collections of debris in the stomachs of catfish. Most catfish, in fact, have taste glands located over much of their body, although these glands are concentrated in their long sensory whiskers.
The North American freshwater catfish family includes the various madtoms, about two dozen of which are in the genus Noturus. All are small, most of them less than 5 inches long. Madtoms are recognized by their unique adipose fin. A non-madtom catfish has a fleshy fin protruding from its back just ahead of the caudal fin. The adipose fin of a madtom is continuous with its caudal fin.
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