Terrence R. Tiersch
For more than seven decades, catfish farmers have relied on the warming of spring to trigger spawning in channel catfish. The necessary water temperatures (75 degrees F to 85 degrees F) for spawning last only a month or two, typically May and June in southern Louisiana, making this a busy time. The farm-raised catfish industry has adapted to this through specialization. Rather than spawn their own fish, most farmers purchase stocking fish, called fingerlings, from suppliers.
Researchers at the LSU Agricultural Center’s Aquaculture Research Station
have been working for the past three years to lengthen and control the catfish spawning season. This work, supported in part by the Louisiana Catfish Promotion and Research Board, involves adding warm water to small ponds (0.1- acre) that contain broodstock channel catfish. By raising the pond temperature, researchers have been able to spawn catfish as early as March, doubling the length of the spawning season. Maintaining ponds within the proper temperature zone can avoid temporary shutdowns of spawning caused by cold snaps. Warming small broodstock ponds early in the spring would produce fry, the newly hatched catfish, that could be raised in the warm ponds to yield large fingerlings early in the season. The increased production of fry and fingerlings could prevent the shortages that have hampered the stocking of catfish in the past. Another benefit of controlling the spawning season is disease prevention. Before catfish reach about 3 inches in length, they are susceptible to diseases including enteric septicemia, a bacterial disease that can destroy stocks of fingerlings. Because this disease proliferates at temperatures above 85 degrees F, it could be controlled by maintaining temperatures in the fry and fingerling ponds (used after the broodstock are removed) at about 80 degrees F. Artificial spawning
Spawning procedures have remained essentially unchanged since the 1920s. Containers are placed into ponds for the catfish to enter and spawn, simulating the natural situation in which channel catfish would spawn in hollow logs or holes in riverbanks. Farmers collect the egg masses from the cans and bring them into the hatchery for fry production. This procedure, although effective for producing large numbers of fish, greatly hampers genetic improvement because it allows only minimal opportunity for selective breeding.
Researchers at the Aquaculture Research Station have improved methods to spawn catfish artificially in the laboratory. At present this technique is limited to use as a research tool because of cost, complexity and dependability. But the technique has potential to move the catfish industry into the era of genetic improvement. Artificial spawning involves large-scale collection of unfertilized eggs from females to allow controlled fertilization with sperm from specific (superior) males. Fingerling producers could specialize in this technology, which is used for most other farmed fishes, and produce a higher quality fish for sale to farmers. The extra expense would be offset by the superior performance of the improved stocks. Developing hybrids
Another advantage of artificial spawning is the ability to develop hybrids. Consider, for instance, the hybrid produced by crossing the female channel catfish with the male blue catfish. This hybrid is considered superior to both parental species in disease resistance, tolerance to low oxygen and uniformity of meat yield. This valuable hybrid is not readily available to producers, however, because the two species do not naturally interbreed. Artificial spawning could produce hybrid fingerlings for the Louisiana catfish industry. The availability of genetically superior catfish would make Louisiana catfish producers more competitive with the larger operations of other states. Raising such fingerlings in heated ponds would round out this picture with a larger, superior fish available for stocking. Freezing sperm
Another important component for genetic improvement, already available for application, is sperm cryopreservation. In 1991, the author produced the world’s first channel catfish from thawed sperm. Since then, the Aquaculture Research Station has developed cryopreservation procedures for sperm of more than 30 species of fish and shellfish. The station also was first in the successful production of a cultured aquatic food species (oysters) from frozen larvae.
Cryopreservation offers many benefits for the catfish industry. Frozen sperm can ensure that particular traits can be reliably produced over extended periods. Sperm from valuable males could be used for years, even long after their death, and could be used to fertilize eggs from many different females in a given year. This would provide the groundwork for selective breeding programs. Storage of frozen sperm is considerably cheaper and, in many ways, safer than maintaining broodstock in ponds, which is expensive and takes up space that could be used for production. Maintaining a large number of different strains of broodstock is prohibitively costly, even to large-scale fingerling producers. In addition, there are many ways to lose valuable catfish broodstock. Some sources of loss can be quite rapid, such as disease outbreaks or low oxygen levels, but broodstock loss can be gradual, too. The insidious loss of genetic integrity by inbreeding or outbreeding depression, for example, can result in poor growth or reproduction.
Clearly, broodstock maintenance can pose significant problems, yet successful genetic improvement of catfish will require the availability of numerous different genetic stocks. Similar problems have been addressed in other agricultural industries such as beef, poultry and pork by freezing sperm. This technology offers obvious advantages in the preservation of desirable genes, in selective breeding, cross-breeding and hybridization, and in standardization of broodstock quality, although it remains unavailable without the use of artificial spawning. More control
Temperature control of ponds is an important component in an overall program to make artificial spawning and genetic improvement available to the Louisiana catfish industry. Our research offers a glimpse into the future in which catfish farming is more controlled by the farmer and more like the predictable production systems already in place in crop and livestock agriculture. The future needs of the channel catfish industry in the coming century are impossible to forecast. The future could bring problems quite different from those of today. New diseases, changes in production systems or different market structures could require specific characteristics of catfish not valued at present. Storage of sperm from numerous stocks could ensure a reservoir of genetic material available for specific genetic improvement. By developing reliable, simple and inexpensive methods for artificial spawning, the Louisiana catfish industry can assume a leading role in genetic improvement and hybridization of catfish and move in step with the beef, pork and poultry industries in protecting, developing and distributing genetic improvementsTerrence R. Tiersch, Professor, Aquaculture Research Station, LSU Agricultural Center, Baton Rouge, La.
Acknowledgments Personnel involved in catfish farming research include Mark Bates, John Buchanan, Michael Christensen, Donald Glenn, Robert Lang, Nyanti Lee, Carmen Paniagua-Chavez, Greg Roppolo, William WaymanandGangYu.
(This article was published in the fall 1999 issue of Louisiana Agriculture.)