64 March 2012 Channel catfish Ictalurus punctatus growth in single and multiple-batch production William A. Wurts1 Research at the University of Arkansas at Pine Bluff (UAPB) indicated that, as stocking density increases in single-batch channel catfish production ponds, the number of market-size fish produced in a single season declines (Southworth et al. 2006a, Engle 2010). The same effect was observed for advanced size stockers as well as smaller juveniles (Figs. 1 and 2). The effect was more pronounced in ponds stocked with smaller juveniles. This suggests that social dominance becomes a significant factor as stocking density increases. As size disparity grows, the effect would be amplified. Because processors and large retail buyers demand specific fish sizes, channel catfish are harvested on the basis of size, using size-selective nets. Fish of desired size are removed, allowing undersize fish to remain and continue growing. To maintain maximum year-round production, catfish fingerlings are periodically stocked with the larger, remaining undersize catfish in multiple-batch production (“under-stocking”). This creates a mixed size-class fish population in production ponds. The combined fish population is fed to satiation with floating feeds that target larger fish. Survival of under-stocked fingerlings has been reported to be around 70 percent but is frequently less (Engle and Stone 2002, SRAC 2007). Survival ranging from 24 to 76 percent (Table 1) was observed in multiplebatch channel catfish research ponds at UAPB (Engle and Valderamma 2001, Southworth et al. 2006b). None of the fingerlings in the UAPB research ponds grew to market size in a single growing season. It is likely that the larger fish already present when fingerlings were stocked were more aggressive at feeding time. The dominant, more aggressive fish consumed more feed than needed, leaving insufficient feed to promote good growth and survival of under-stocked fingerlings. Fingerling growth is exponential. They grow significantly faster and require more feed per unit of body weight than 0.4-0.6 kg catfish. Feed deprivation slows fingerling growth during this critical period of the production cycle. As a result, they do not reach market size during a single production season. Larger and near foodsize catfish are stronger and more aggressive. It is unlikely that under-stocked fingerlings can compete effectively with larger fish for bigger, floating feed pellets (Tucker et al. 1994, Wurts 2001). If 1400-3500 kg/ha of large 0.4-0.6 kg fish are crowding out smaller fingerlings at mealtime, Fig. 1. Percent under-size channel catfish harvested from single batch production ponds stocked at three densities ranging from 2480 to 7440 fish per hectare (adapted from Engle, 2010).* * Individual fish less than 1.36 kg were considered under-size at harvest. * Individual fish size at stocking was 0.36 kg. Fig. 2. Percent under-size channel catfish harvested from single batch production ponds stocked at four densities ranging from 8600 to 34600 fish per hectare (adapted from Southworth et. al. 2006b).* * Individual fish less than 0.57 kg at harvest were considered under-size. * Mean individual fingerling size at stocking was 16 g. * Survival ranged from 67 to 83 % with a mean of 73 percent.
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