WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 37 (CONTINUED ON PAGE 38) treatments were able to accelerate sexual maturation in juvenile male white bass and improve markers of fecundity in adult female white bass (Beck et al. 2012a). To date, this is the first description of kisspeptin-mediated pubertal initiation in fish and the first evidence that kisspeptins could potentially improve fecundity. Although it remains to be determined how kisspeptins may best be applied in commercial practice, our findings are driving studies to characterize the molecular underpinnings of the KISS system in various foodfish species to improve reproductive output on farms. The Physiology Team at SNARC is also interested, particularly, in the study of mucosal health in fish. Mucosal surfaces, such as the skin, gill and intestine, function as the first line of defense against pathogen invasion and simultaneously carry out a diverse array of other critical physiological processes, including nutrient uptake, osmoregulation and waste excretion. Aquaculture species depend more heavily on mucosal barriers than terrestrial animals because they are continuously interacting with the microbiota of the aquatic environment. Currently our group is studying mechanisms by which pathogenic bacteria adhere to and gain entry into fish through mucosal surfaces. Our principal disease focus in this context is columnaris disease, caused by the bacterium Flavobacterium columnare, which is an opportunistic pathogen that causes substantial mortality globally in freshwater ornamental and foodfish species. Despite the obvious importance of this disease, until very recently, little was known regarding how F. columnare bacterial cells actually adhere to and initiate disease in host fish. In this regard, our group has made tremendous progress in this area by employing cutting-edge next-generation sequencing (RNA-seq) and microarray techniques that have allowed the identification of many early molecular immune events that control the susceptibility/resistance of fish to columnaris and other bacterial diseases (Li et al. 2013a, Li et al. 2013b, Peatman et al. in press). One such discovery was the identification of a new receptor used by F. columnare cells for attaching to the gills of catfish, termed a rhamnose-binding lectin (RBL, Beck et al. 2012b). Briefly, in catfish susceptible to columnaris disease, RBL was strongly up-regulated within the gills of susceptible fish after challenge with F. columnare. Moreover, blocking of the receptor with its natural carbohydrate ligands, L-rhamnose, outcompeted bacterial cells for RBL binding sites and resulted in significantly decreased columnaris disease mortality. Importantly, the expression of RBL was tightly linked to nutritional status, with fasted fish having much higher RBL expression than fed fish and, presumably, a heightened susceptibility to columnaris disease. Clearly, these findings emphasize the importance of the RBL compartment in columnaris disease and position RBLs as key targets for intervention, particularly in the context of vaccinemediated strategies aimed at columnaris disease prevention. office buildings, and other support buildings and was administered by the U.S. Fish and Wildlife Service. Over the subsequent 50+ years, FFEL grew and in 1992 the newest building was opened, a $5.6 million research laboratory and office building, consisting of 1,400 m2 of space for research (60 percent) and office space (40 percent) for employees. In 1996, FFEL was transferred to the USDA-ARS and was renamed SNARC. Because extension is not within the purview of the ARS, diagnostic and extension activities were ended in 1998 and, in 1999, SNARC was renamed for the long-time director Harry K. Dupree. Other directors of the FFEL or HKDSNARC were James Stevenson (1961-1965), Kermit Sneed (1965-1973), and Don Freeman (2000-2011). SNARC has had its highs and lows since its construction. In 1974, FFEL employed 23 full-time employees, but by 1983, this had declined to 9. Today, SNARC has 24 personnel including 8 research scientists, 1 ARS scientist, 2 support scientists, 8 technicians, and 5 administrative and facilities support staff. Research Activities The following are summaries of the research programs at SNARC and brief synopsis of current research conducted at the Center. Using Molecular Physiology to Address Barriers in Reproduction and Immunity Irrespective of fish species, one of the major factors limiting further development of the U.S. aquaculture industry is the lack of a reliable supply of seed (i.e. fingerlings), a problem largely stemming from obstacles in captive breeding, such as delayed puberty and poor fecundity or fertility. The time at which fish reach sexual maturity is an important parameter for commercial aquaculture operations because the delay or failure of fish to sexually mature requires long-term maintenance of broodstock on farms, dramatically increasing husbandry costs and exposure of the broodfish to risks associated with stress and disease. Alternatively, exceptionally early (precocious) sexual maturation can negatively affect growth, feed utilization, health and animal welfare, inasmuch as energy is diverted from growth. To address these problems, an understanding of the fundamental molecular mechanisms associated with sexual maturation and fertility in farmed fish is needed, an area poorly understood when compared to other livestock. The Physiology Team at SNARC is confronting issues in reproductive biology by employing various molecular, cellular and next-generation sequencing approaches to identify key genetic regulators of sexual maturation in white bass Morone chrysops, striped bass M. saxatilis, and blue catfish Ictalurus furcatus to improve reproductive yields from broodstock. Recent research by our group examined the effects of the administration of small 10-amino acid peptides to fish, termed kisspeptins (the products of the KISS1 and KISS2 genes; Fig. 1), which have been shown to control the development of puberty in mammals. Kisspeptin Irrespective of fish species, one of the major factors limiting further development of the U.S. aquaculture industry is the lack of a reliable supply of seed (i.e. fingerlings), a problem largely stemming from obstacles in captive breeding, such as delayed puberty and poor fecundity or fertility.
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