Members of the order Siluriformes arefound in fresh and salt water worldwide. There are at least 39species of catfish in North America, but only seven have beencultured or have potential for commercial production. They arethe blue catfish, Ictalurus furcatus (LeSueur); the whitecatfish, Ictalurus catus (Linnaeus); the black bullhead,Ictalurus melas (Rafinesque); the brown bullhead, Ictalurusnebulosus (LeSueur); the yellow bullhead, Ictalurus natalis(LeSueur); and the flathead catfish, Pylodictis olivaris(Rafinesque).
Distribution
Channel catfish were originally found only in the GulfStates and the Mississippi Valley north to the prairie provincesof Canada and Mexico, but were not found in the Atlanticcoastal plain or west of the Rocky Mountains. Since thenchannel catfish have been widely introduced throughout theUnited States and the world.
Physical characteristics
Like all native North American catfishes, a channel catfishhas a body that is cylindrical in cross-section, and lacksscales. Fins are soft-rayed except for the dorsal and pectoralfins which have sharp, hard spines that can inflict a nasty,painful wound if a catfish is handled carelessly. An adipose fin(lacking rays) is located on the back betweenthe dorsal and caudal fins (Figure1). One conspicuous characteristic of allcatfish is the presence of barbels aroundthe mouth. The barbels are arranged in adefinite pattern with four under the jawand one on each tip of the maxilla (upperjaw).
The channel catfish is the only spottedNorth American catfish with a deeplyforked tail. There are 24-29 rays in theanal fin. They are generally olivaceous toblue on the back, shading to the off-whiteventrally.Their color, to a large extent, is dictatedby the color of the water they inhabit.In clear water they may appearalmost black, while in muddy water theymay be a light yellow. Young channelcatfish are irregularly spotted on their sides, but the spots tendto disappear in the adults.
Figure 1: External parts of the Channel Catfish
Habitat
In natural waters, channel catfish live in moderate toswiftly flowing streams, but they are also abundant in largereservoirs, lakes, ponds, and some sluggish streams. Theyare usually found where bottoms are sand, gravel, or rubble,in preference to mud bottoms. They are seldom found indense aquatic weeds. Channel catfish are freshwater fish butthey can thrive in brackish water.
Channel catfish generally prefer clear water streams, butare common and do well in muddy water. During the day theyare usually found in deep holes wherever the protection oflogs and rocks can be found. Most movement and feedingactivity occurs at night just after sunset and just beforesunrise. Young channel catfish frequently feed in shallow riffleareas while the adults seem to feed in deeper water immediatelydownstream from sand bars. Adults rarely move muchfrom one area to another and are rather sedentary, whileyoung fish tend to move about much more extensively,particularly at night when feeding.
Feeding
Feeding can occur during day or night, and they will eata wide variety of both plant and animal material. Channelcatfish usually feed near the bottom in natural waters but willtake some food from the surface. Based on stomach analysis,young catfish feed primarily on aquatic insects. The adultshave a much more varied diet which includes insects, snails,crawfish, green algae, aquatic plants, seeds, and small fish.When available, they will feed avidly on terrestrial insects, andthere are even records of birds being eaten. Fish become animportant part of the diet for channel catfish larger than 18inches total length, and in natural waters fish may constituteas much as 75 percent of their diet.
Channel catfish primarily detect food with their sense oftaste. Taste buds are found over the entire external surface ofcatfish as well as inside the mouth, pharynx, and gill arches.They are most numerous on the barbels and gill arches. Inclear water, eyesight can be an important means of findingfood. However, in turbid water, taste is the primary way catfishlocate food. The organ of smell (olfactory organs) may playsome role, but this has not been well established. Theolfactory organs are found in the nostrils (nares), which arelocated on top of the head just in front of the eyes.
Age and growth
Channel catfish grow best in warm water with optimumgrowth occurring at temperatures of about 85° F (29.4° C).With each 18° F (10° C) change in temperature there is adoubling or halving of their metabolic rate. This means thatwithin limits, their appetite increases with increasing watertemperatures or decreases with decreasing water temperatures.In natural waters, the average size channel catfish caughtby fishermen is probably less than 2 to 3 pounds, but the worldrecord of 58 pounds was caught in Santee Cooper Reservoir,South Carolina, in 1964. The size and age that channel catfishreach in natural waters depends on many factors. Age andgrowth studies have shown that in many natural waterschannel catfish do not reach 1 pound in size until they are 2to 4 years old. One study in the Lake of the Ozarks, Missouri,found that channel catfish did not reach a size of 13 inchestotal length until they were 8 years old. The maximum age everrecorded for channel catfish is 40 years, whereas mostcommercially raised catfish are harvested before they are 2years old.
In production ponds the growth rate of channel catfish isdetermined by water temperature; length of time held atdifferent water temperatures; quantity and quality of food fed;palatability, or taste of food; frequency of feeding; waterquality, etc. Most farm-raised catfish are harvested at a weightof 11/4 pounds at an age of about 18 months.
Water Quality
Water quality preferences and limitations for wild channelcatfish are not any different from those of farm-raised channelcatfish. The lethal oxygen level for both wild and farm-raisedcatfish is about 1 ppm, and reduced growth occurs at oxygenconcentrations of less than 4 ppm. Channel catfish, in naturalwaters, are no more tolerant of high levels of ammonia andnitrites than are farm-raised catfish, but are seldom exposedto lethal concentrations of either ammonia or nitrite.
Respiration
Figure 2: Schematic drawing of fish gills.
Like other animals, channel catfish need oxygen to live. They use oxygen for energy production and to help build all the various parts of the body. However, oxygen is at most only about 25 percent as abundant in water as in the air. To get oxygen, fish must expend more energy than air-breathers. Fortunately, fish have well developed breathing organs, the gills. Although catfish live in the water, gills serve essentially the same functions as our lungs to take oxygen from the external environment and to rid the body of toxic gaseous waste, carbon dioxide (CO2). Water passes over the gill surface where oxygen diffuses into the blood and carbon dioxide diffuses out.
The gills of channel catfish are located on each side of the head (Figure 2) and they are covered by a protective movable flap of skin called the gill flap or operculum. There are four gills on both sides of the head, each consisting of a double row of slender gill filaments.
These filaments are supported by a flexible white gill arch. Each side of the filament has many thin, small cross plates called lamellae. It is across the gill lamellae that the important respiratory gases are exchanged (Figure 3). Each gill and gill filament has a rich supply of blood vessels which carries blood from the heart to the gills and then throughout the fish. The lamellae have spaces through which blood rapidly percolates. Oxygen that is picked up at the gill lamellar surface is carried throughout the body in the blood. Waste carbon dioxide is also carried in the blood for release into the water at the lamellar surface.
Figure 3: Schematic drawing of gill filament.
A fish breathes by sucking water in through the mouthwhere it flows directly over the gill filaments and across thelamellae. Blood channeled through the heart has a low oxygenconcentration, but at the gill lamellae surface it passes nearwater high in oxygen. By simple diffusion, oxygen crosses thegill surface and enters the blood where it is carried throughoutthe fish. Respiration of this type is called counter-currentexchange. Simple diffusion of oxygen through the gill lamellaeand into the blood occurs because the gill lamellae areextremely thin.
Carbon dioxide is released from fish in much the sameway oxygen is taken in by counter-current exchange. Bloodhigh in carbon dioxide is channeled through the heart to thegills where it comes in close contact with water low in carbondioxide. By simple diffusion carbon dioxide is then releasedinto the water.
Depending on the needs of the fish, the rate of breathingmay be variable. Fish that are stressed or are pursued by apredator have a greater oxygen demand than fish at rest.Similarly, if the oxygen concentration in the water is low, a fishhas to breathe faster if it is to meet all of its oxygen requirements.During normal respiration only about 60 percent of thegill surface is used for gas exchange. During increased respiratorydemands, up to 100 percent of the gill surface may beused.
It is easy to see that any alteration in gill structure orfunction can be dangerous to catfish. Any increase in thethickness of the gill lamellae will decrease the efficiency of gasdiffusion. If the gills become swollen or puffy, oxygen andcarbon dioxide transfer are decreased. Gills can becomethickened following exposure to ammonia, certain vitamindeficiencies, or to long-term parasite or bacterial infestations.Any type of toxic agent which damages the gill filaments orlamellae will also affect the efficiency of gas exchange. Finally,if a fish is anemic or has brown blood disease, even though thegills are not damaged and there is adequate oxygen in thewater, the blood may not be able to carry enough oxygen toensure survival.
Spawning
Channel catfish spawn when the water temperature isbetween 75° and 85° F (23° to 30° C) with about 80° F (27° C)being optimum. Wild populations of catfish may spawn asearly as late February or as late as August depending on thelocation. The length and dates of the spawning season varyfrom year to year depending on the weather and area, butpeak spawning time in Mississippi usually occurs in May.Channel catfish are cavity spawners and will spawn onlyin secluded, semi-dark areas. In natural waters male catfishwill build a nest in holes in the banks, undercut banks, hollowlogs, logjams, or rocks. It is this behavior that necessitates theuse of spawning containers in order to successfully spawnchannel catfish in commercial ponds.
The male selects and prepares the nest by fanning out asmuch mud and debris as possible. He will then defend thislocation against any intruder until spawning is completed andthe fry leave the nest. The female is attracted to the nest andspawning occurs within the nest with eggs being laid in agelatinous mass on the bottom. After the eggs are laid, themale takes over and cares for the eggs by constantly fanningthem with his fins to provide aeration and to remove wasteproducts given off by the developing eggs.
Females spawn only once a year, producing about 3,000to 4,000 eggs per pound of body weight, while the males mayspawn more than once. In wild populations, males seldomspawn more than once a year, but in hatcheries where theeggs are removed from the spawning container soon afterbeing laid, males may spawn 3 or 4 times; and there is a recordof one male spawning nine females in one season. Channelcatfish usually become sexually mature at 3 years of age,although some may spawn when 2 years old. In wild populationsthey may not spawn until after the age of 5 years.
Channel catfish weighing as little as 3/4 of a pound may spawnif old enough, whereas farm-raised catfish usually weigh inexcess of 2 pounds when they spawn. After the eggs are laidthey will usually hatch in 5 to 10 days depending on watertemperature. At 78° F (26° C) the eggs will hatch in about 8days. For each 2° F (1° C) rise in temperature above 78° F,subtract 1 day, and for each 2° F (1° C) fall in temperaturebelow 78° F, add 1 day to get the approximate length of timerequired for hatching. Water temperatures below 65° F (18° C)and above 85° F (30° C) will reduce hatching success. Newlyhatched fry have a large yolk sac which contains the nourishmentthey need for the next 2 to 5 days until they are fullydeveloped and are ready to start feeding. After the yolk sacis absorbed, the fry take on their typical dark color and willbegin to swim-up looking for food. At first swim-up fry will gulpair to fill their swim bladders which helps them maintain andregulate their buoyancy. Originally published on the Southern Regional Agricultural Center and the Texas Aquaculture Extension Service (February 2006)
