Location: Warmwater Aquaculture Research Unit2010 Annual Report
1a. Objectives (from AD-416)
1) Identify mechanisms and develop tools and methods to improve growth efficiency of catfish. 2) Determine mechanisms of host-pathogen interactions and sources of variation in catfish immune function to improve catfish health and survival. 3) Improve efficiency of channel and blue catfish reproduction and channel x blue hybrid production. 4) Identify genomic regions affecting variation in traits of economic importance through quantitative trait locus (QTL) discovery and fine mapping strategies. 5) Develop, and transfer to commercial producers, channel catfish and blue catfish germplasm improved for growth, yield, and disease resistance for improved production of channel, blue and hybrid catfish.
1b. Approach (from AD-416)
To attain the first objective, we will correlate mitochondrial functional variation with catfish feed efficiency and identify and determine the role of specific genes and gene products (peptides and proteins) involved in controlling growth in catfish. For the second objective, we will construct a catfish microarray targeted toward immune function, characterize functional genetic variation in resistant vs. susceptible channel catfish, and characterize the effect of prebiotic administration on catfish immune function. For the third objective we will induce early maturation in channel catfish and blue catfish through compressed annual temperature cycles, increase ovulation and fertilization efficiency for production of blue X channel F1 hybrid catfish, and establish a technique for spematogonial transplantation between blue and channel catfish. For the fourth objective we will enhance and integrate genetic and physical maps, and identify quantitative trait loci associated with superior production traits, especially carcass traits and survivability to E. ictaluri infection. For the fifth objective, we will produce a line of select channel catfish based on multi-trait selection within a commercial composite population, produce a line of select blue catfish based on males that produce hybrid offspring with superior growth and carcass yield, and produce male channel and blue catfish which have a YY sex chromosome complement for all male catfish production.
3. Progress Report
Cryopreserved sperm from 20 blue catfish from two strains were used to fertilize eggs from channel catfish to initiate evaluation of the effects of blue catfish germplasm on hybrid performance. Growth and fillet yield of 190 families of channel catfish is being evaluated as part of the Catfish Genetics Research Unit (CGRU) breeding program. Catfish from multiple studies were analyzed for processing yield at the CGRU processing facility for cooperators at Mississippi State University and the University of Arkansas Pine Bluff (an 1890s institution) to determine impact of altering diet composition on processing yield. Fingerling channel x blue hybrid catfish were stocked at five different densities to determine effects of stocking density on growth, feed conversion, fillet yield, and survival because effects of density on production are not well documented for hybrid catfish. Five replicate groups of 10 similarly aged full-sib channel catfish families (a total of 50 families) are being reared in different competitive environments to determine effects of environment of growth rankings of families. The 3-5 year generation interval of blue catfish slows progress in selective breeding. Investigations are underway to use controlled temperature cycling in tanks to shorten the time to sexual maturation. Blue catfish fry were hormonally feminized by feeding estrogens for 3 weeks during neonatal development to produce female blue catfish with an XY sex genotype. These fish will be used to produce YY males which would, in turn, produce all male offspring for use in hybrid catfish production. Intracranial and ovarian lavage methods of hormone delivery methods were evaluated for hybrid catfish production to improve the efficiency of induce spawning in channel catfish females. Improvements were made on hybrid fry production protocols (broodfish selection, egg treatments, harvesting methods) in commercial hatcheries. Maternal transfer of vitamin C was assessed for reproductive performance in channel catfish and subsequent hybrid progeny performance was evaluated for growth, disease resistance and stress response for low dissolved oxygen. Pond trials were conducted to determine the response of five levels of dietary lipids on the reproductive performance of channel catfish in hybrid catfish production. DNA sequence was produced from pooled catfish DNA for identification of single nucleotide variants. The insert lengths of clones in a random-sheared large-insert DNA library were too variable to provide high quality information for enhancement of the catfish physical map. Alternate methods are now under evaluation for organizing joined DNA fragments (contigs) as chromosomes. Broodstock from 10 families with high levels of survival to Edwardsiella (E.) ictaluri challenge were used to produce channel and hybrid catfish families to assess the genetic components of disease resistance. Details of subprojects can be found in 6402-31000-009-01N, 6402-31000-009-03S, 6402-31000-009-07R, and 6402-31000-009-08R.
1. Factors Influencing Spawning Success in Channel Catfish. Spawning success of channel catfish in ponds is highly variable and factors influencing spawning are not understood. A better understanding of factors influencing spawning will improve spawning success and reduce production costs. DNA markers were used to identify parentage of spawns from a mixture of broodfish from 8 different commercial farms. Approximately 30% of two year old females and 50% of 3 year old females spawned and spawns were collected for over a 100 day period each spawning season. Plasma hormone levels, ultrasound estimates of ovary size, and farm of origin were not predictive of either spawning time or incidence in either spawning season. Females from 2 farms consistently spawned earlier than females from other farms, and time of spawning was positively correlated across years for females suggesting a genetic basis for spawning time in female catfish and the possibility of altering spawning time through selection.
2. Commercial Production of Channel x Blue Hybrid Catfish Fry. Hybrid catfish have demonstrated excellent performance for several important traits but commercial production of hybrid fry is complicated and novel to most commercial catfish hatchery operators. In 2010, Catfish Genetics Research Unit (CGRU) scientists made several visits to the four commercial hatcheries currently producing hybrid catfish fry to give advice, demonstrate techniques and collect data on production of hybrid fry. Transfer of hybrid production technology to catfish fingerling producers is expected to improve production efficiency via an increased supply of hybrid catfish fingerlings to growers.
3. Use of Bromelain to Remove Adhesiveness of Catfish Eggs and Improve Hatch at a Commercial Hatchery. Manual spawning of catfish required for hybrid catfish production typically results in less than optimal fertilization and unfertilized eggs degrade and reduce hatch. ARS researchers in Stoneville, MS, previously determined the concentration, time of application, and duration of application of the enzyme bromelain to prevent adhesion of catfish eggs after fertilization. Large scale versions of standard hatching jars for use on large number of eggs were developed and successfully used at a commercial hybrid catfish hatchery. Commercial hatchery managers reported improved hatching success and two additional commercial hatcheries have indicated they will use the jar hatching technique next year for hybrid catfish production.
4. Effects of Stocking Density on Production Traits of Channel Catfish and Channel Catfish x Blue Catfish Hybrid Fingerlings Split During First Growing Season. Channel and hybrid catfish fingerlings were stocked in early July at densities of 25,000 and 50,000 fish per acre to determine effects of genotype and density on production traits. Hybrids were larger at stocking and harvest than channel catfish of similar age. Hybrid and channel catfish had similar survival and feed conversion. Fish grown at lower densities had faster growth, higher survival and better feed conversion.
5. Evaluation of Pre- and Probiotics for Improving Catfish Production. Losses to disease lead to significant losses in catfish production so practical approaches are needed to improve catfish immunity. Studies conducted by ARS scientists at Stoneville, MS, showed that feeding one prebiotic led to improved channel catfish survival after challenge with a virulent bacterial pathogen. A second study showed the prebiotic led to a 15% increase in weight gain. One probiotic study, in which channel catfish were fed three microbial products for nine weeks, was conducted in collaboration with University of Arkansas. There was no improvement in weight gain or survival of catfish challenged with Edwardsiella (E.) ictaluri. Future studies will address the mechanisms of action of how prebiotics influence growth and disease resistance of channel catfish.
6. Large Scale Identification of Single Nucleotide Variations in the Catfish Genome. In order to more efficiently use indirect selection of catfish broodstock based on genetic potential, a large number of DNA sequence variants are needed to serve as proxy markers for functional genetic variants throughout the genome. This research utilized high-throughput sequencing of DNA fragments from multiple catfish, and the DNA sequences were aligned to permit efficient detection of single nucleotide variations between individuals. There were 37,764 genomic locations interrogated, and 6,640 contained a sequence variant in this sample population. Further testing showed 93% of the predicted variable loci were variable in the individuals, and the predicted and realized allele frequencies were strongly correlated. The research identified 9,674 high-likelihood DNA sequence variants that will be useful for catfish identification, population structure, and selective breeding.
7. Regulation of Feed Intake in Catfish. Hormonal factors that control feed intake are not well understood in catfish. Therefore, ARS scientists in Stoneville, MS, conducted research to investigate the role of four neuropeptides, ghrelin, neuropeptide Y (NPY), cholecystokinin (CCK), and cocaine and amphetamine-regulated transcript (CART), in the regulation of feed intake in channel catfish. Ghrelin and NPY gene activities increased prior to a meal and decreased 2 hours later while CCK and CART gene activities were low prior to a meal but increased 1 hour after the fish had eaten. These results indicated that ghrelin and NPY stimulated feed intake while CCK and CART depressed intake. Understanding the hormonal control of feed intake will help researchers develop strategies to improve feed efficiency in catfish.
8. Efficient Production of All-male Catfish Populations. Matings of sex-reversed female catfish with normal XY males can produce XX female offspring, and XY and YY male offspring. However, XY and YY males are physically identical, so these males must be mated with normal XX females to measure the sex ratio of offspring (YY males will produce all male offspring). ARS researchers in Stoneville, MS, developed DNA markers to identify the X or Y chromosomes in 3 families of channel catfish, and performance testing of 2 yr old males verified the rapid DNA test could be used to identify XY females and YY males without the need for progeny testing. This research will improve the efficiency of YY male production for production of all male populations for production trials.
5. Significant Activities that Support Special Target Populations
The USDA Census of Aquaculture conducted in 2000 classified 84% of catfish farms as small businesses, with annual sales of less than $500,000. Of the 1,370 catfish farms in the United States, 38% (515) reported annual revenues of less than $25,000. This data is not available in the 2005 Census of Aquaculture. Increased foreign competition and higher feed and fuel prices have reduced the profit margins for these small businesses. Development of catfish lines with superior performance for commercially important traits, utilization of these lines in commercial culture, and utilization of production technology originating from the Catfish Genetics Research Unit will help solve production problems, increase efficiency and profitability for both small and large catfish farmers, and provide a quality product for consumers. Most catfish producers with limited acreage buy fingerlings from large breeders that are very likely to utilize improved brood stocks, and the development and use of improved catfish lines can quickly affect the profits of small producers. Because small farms do not enjoy the same economies of scale experienced by larger operations, breeding fish with improved production traits will be highly beneficial to small farmers. Average consumers also benefit from the increased availability of higher-quality, safer domestic products at a reduced price.
Wang, S., Peatman, E., Abernathy, J., Waldbieser, G.C., Lindquist, E., Richardson, P., Murdock, C.A., Small, B.C., Quiniou, S., Liu, Z. 2010. Assembly of 500,000 Inter-Specific Catfish Expressed Sequence Tags and Large Scale Gene-Associated Marker Development for Whole Genome Association Studies. Genome Biology. 11:R8.