38 DECEMBER 2013 • WORLD AQUACULTURE • WWW.WAS.ORG Selective Improvement of Hybrid Striped Bass Broodstock One of the problems facing the striped bass and hybrid striped bass (Fig. 2) aquaculture industry is the lack of selectively-improved, domesticated broodstock. Currently most fingerling producers use wild-source broodstock to produce fingerlings that are supplied to growers. This has resulted in tremendous yearto-year performance differences, concerns regarding maintenance of a reliable broodfish and fingerling supply, increased regulatory pressure on interstate transport of sportfish grown for foodfish markets and increasing disease issues. The National Hybrid Striped Bass breeding program is located at SNARC and, with partner research scientists at North Carolina State University, is developing broodstock and testing progeny from hundreds of distinct crosses from multiple geographic stocks of striped bass and white bass. These families have been and continue to be selected for rapid growth and other attributes, such as susceptibility to disease, in freshwater ponds and tanks. Recent studies have determined heritability of growth-related traits in white bass (Fuller and McEntire 2011) and hybrid striped bass (Fuller et al. 2013) fry and fingerlings in ponds and tanks. Domestication of striped bass and white bass allows greater control over the reproductive cycle and spawning conditions. Domestication also allows choices related to age, size, and the duration of the reproductive photothermal period. The choices made may affect the success of induced spawning efforts. For example, choosing older or larger individuals might affect fertilization or hatching rates or size of individuals at hatch or at yolk absorption. Quantifying these factors could lead to improvements in hatchery efficiency during production of hybrid striped bass. In collaborative research with the University of Arkansas at Pine Bluff, a series of studies were initiated at SNARC to determine the impact of female weight and age on larval length. Female weight and age (phenotype) have limited influences on length 5 days post-hatch, when the effect is mostly based on the genetic makeup of the parents (genotype). If heritability of length at 5 days post-hatch is sufficient, then selection for this trait could increase the size of larvae. This is important because, if sufficiently large, larvae might be able to consume Artemia nauplii as a first food, eliminating the current requirement for rotifers. This has the potential to significantly change the economics of tank culture of fingerling hybrid striped bass and lead to yearround availability of fingerlings. Geneticists are also employing next-generation sequencing technologies to better understand the factors controlling such traits as growth, response to hypoxia and disease resistance, all of which will benefit from molecular profiling of underlying changes in gene expression. Genomic knowledge of striped bass, white bass and its hybrids currently lags behind those of other aquaculture species. Existing genomic knowledge consists of a medium-density genetic linkage map (Liu et al. 2012) and a wellannotated ovarian transcriptome (Reading et al. 2012). To increase genomic resources available to Morone researchers, SNARC scientists, in collaboration with the Aquatic Genetics and Genomics Laboratory at Auburn University, are developing the first multitissue white bass and striped bass reference transcriptomes. This new genomic resource will aid government, university, and industry partners by providing all interested parties an online resource for comparative purposes in future genomics studies and providing species-specific primer sets for analysis of key genes. Increased Production System Efficiency Biofloc technology (BFT) or mixed, suspended-growth production systems are being used more frequently worldwide for culturing various aquatic animals because of the high yields per unit water volume that are possible, resulting in improved efficiency of water use. Technologically this production system is intermediate between earthen pond and recirculating aquaculture systems. In outdoor BFT production systems, a complex of living organisms is closely associated with particulate organic matter and is maintained in suspension by continuous aeration. Oxygen, typically the first factor that limits aquaculture production, is maintained at adequate concentration because of the continuous aeration used to maintain the biofloc in suspension. Waste ammonia excreted by intensivelyfed culture animals, the second limiting factor to aquaculture production, is metabolized by phytoplankton and bacteria, which are part of this complex of living organisms. Scientists at SNARC are evaluating the BFT system for intensification of channel catfish Ictalurus punctatus production (Fig. 3). Research is directed towards optimizing stocking rate and biomass density to produce market-size or stocker-size catfish in one season and evaluating associated effects on water quality; on estimating primary productivity to understand the role of phytoplankton in nitrogen dynamics during the production cycle; and on managing solids levels in the system and how this impacts TOP, FIGURE 2. Photo of hybrid striped bass. BOTTOM, FIGURE 3. Biofloc technology production tanks used to culture channel catfish.
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