Jeffrey T. Silverstein

The Effects of NPY and Insulin on Food Intake Regulation in Fish

Synopsis. Recent abundant studies report that in rodents starvation induces increased neuropeptide Y (NPY) mRNA expression and peptide secretion in the hypothalamus which reduces autonomic nervous activity and promotes food intake, and intracerebroventricular (ICV) injection of NPY has potent orexigenic effects. Conversely, the effect of insulin in the central nervous system is to inhibit food intake and NPY biosynthesis and secretion. In mammals body fatness is regulated and insulin acts as one intake inhibitory signal related to fatness. In salmon (Oncorhynchus sp.) we have demonstrated a rise in NPY-like mRNA expression and a coincident decrease in plasma insulin levels during 2 to 3 weeks of starvation. Additionally, experimentally manipulating body fatness with high and low fat diets has demonstrated that body fatness affects food intake in teleost fishes, raising the possibility that NPY and insulin act to regulate their food intake. Therefore, we hypothesized that as in rodents, ICV treatment with NPY would stimulate food intake while ICV insulin would reduce food intake. Preliminary results suggest that ICV NPY administration does stimulate food intake in channel catfish (Ictalurus punctatus), but central injection of insulin has no effect. Results of treatments with the sulfated octapeptide of cholecystokinin and the recombinant fragment of rat leptin 22–56 are also discussed.

Spleen Size Predicts Resistance of Rainbow Trout to Flavobacterium psychrophilum Challenge

Selective breeding of animals for increased innate resistance offers an attractive strategy to control disease in agriculture. However, this approach is limited by an incomplete knowledge of the heritability, duration, and mechanism(s) of resistance, as well as the impact of selection on the immune response to unrelated pathogens. Herein, as part of a rainbow trout broodstock improvement program, we evaluated factors involved in resistance against a bacterial disease agent, Flavobacterium psychrophilum. In 2005, 71 full-sibling crosses, weighing an average of 2.4 g, were screened, and resistant and susceptible crosses were identified. Naive cohorts were evaluated at 10 and 800 g in size, and most maintained their original relative resistant or susceptible phenotypes, indicating that these traits were stable as size increased >300-fold. During the course of these studies, we observed that the normalized spleen weights of the resistant fish crosses were greater than those of the susceptible fish crosses. To test for direct association, we determined the spleen-somatic index of 103 fish crosses; created high, medium, and low spleen-index groups; and determined survival following challenge with F. psychrophilum or Yersinia ruckeri. Consistent with our previous observations, trout with larger spleen indices were significantly more resistant to F. psychrophilum challenge; however, this result was pathogen-specific, as there was no correlation of spleen size with survival following Y. ruckeri challenge. To our knowledge, this is the first report of a positive association between spleen size and disease resistance in a teleost fish. Further evaluation of spleen index as an indirect measure of disease resistance is warranted.

Rainbow trout resistance to bacterial cold-water disease is moderately heritable and is not adversely correlated with growth.

The objectives of this study were to estimate the heritabilities for and genetic correlations among resistance to bacterial cold-water disease and growth traits in a population of rainbow trout (Oncorhynchus mykiss). Bacterial cold-water disease, a chronic disease of rainbow trout, is caused by Flavobacterium psychrophilum. This bacterium also causes acute losses in young fish, known as rainbow trout fry syndrome. Selective breeding for increased disease resistance is a promising strategy that has not been widely used in aquaculture. At the same time, improving growth performance is critical for efficient production. At the National Center for Cool and Cold Water Aquaculture, reducing the negative impact of diseases on rainbow trout culture and improving growth performance are primary objectives. In 2005, when fish averaged 2.4 g, 71 full-sib families were challenged with F. psychrophilum and evaluated for 21 d. Overall survival was 29.3% and family rates of survival varied from 1.5 to 72.5%. Heritability of postchallenge survival, an indicator of disease resistance, was estimated to be 0.35 +/- 0.09. Body weights at 9 and 12 mo posthatch and growth rate from 9 to 12 mo were evaluated on siblings of the fish in the disease challenge study. Growth traits were moderately heritable, from 0.32 for growth rate to 0.61 for 12-mo BW. Genetic and phenotypic correlations between growth traits and resistance to bacterial cold-water disease were not different from zero. These results suggest that genetic improvement can be made simultaneously for growth and bacterial cold-water disease resistance in rainbow trout by using selective breeding.

Report of the Plant Products in Aquafeed Strategic Planning Workshop: An Integrated, Interdisciplinary Research Roadmap for Increasing Utilization of Plant Feedstuffs in Diets for Carnivorous Fish

This article was downloaded by: [Bellis, Diane]On: 24 November 2008Access details: Access Details: [subscription number 905736162]Publisher Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Cortisol Response to a Crowding Stress: Heritability and Association with Disease Resistance to Yersinia ruckeri in Rainbow Trout

Abstract The U.S. Department of Agricultures National Center for Cool and Cold Water Aquaculture is conducting a breeding program for rainbow trout Oncorhynchus mykiss to develop improved germplasm for the U.S. aquaculture industry. Current selection efforts are focused on growth and disease resistance, but stress response is also a concern. Using plasma cortisol concentrations after a 3-h crowding stress as a measure of stress responsiveness, we have previously shown family variation in cortisol responsiveness and a positive phenotypic correlation between poststressor cortisol level and growth performance within our broodstock. Selection for improved growth performance may therefore increase cortisol responsiveness to stress. In the present studies, narrow-sense heritability (h 2) for cortisol responsiveness was estimated to be moderately high by means of midparent–offspring regression and nested family design analyses (h 2 ≥ 0.40 and 0.56, respectively). In addition, fish from the same families were us...

Evaluation of a Stress Response for Use in a Selective Breeding Program for Improved Growth and Disease Resistance in Rainbow Trout

Abstract A breeding program to develop improved germplasm for the U.S. rainbow trout Oncorhynchus mykiss aquaculture industry is being conducted at the U.S. Department of Agricultures National Center for Cool and Cold Water Aquaculture. Although current selection efforts are based on growth and disease resistance, stress responsiveness is also a concern. Previous work has shown that heritable differences in stress response can be identified by measuring blood levels of cortisol after exposure to a 3-h crowding stress. We characterized this stress response and measured plasma glucose concentrations in 64 of our broodstock families. We found the method reliable for identifying differences in this stress response. Values for both cortisol and glucose response were similar for replicates of families. The size of the fish within the range examined and the sex of the animals, which were reproductively immature, did not appear to affect response. Variation in poststressor plasma cortisol and glucose was observe...

Relationships among Feed Intake, Feed Efficiency, and Growth in Juvenile Rainbow Trout

Abstract Improving the efficiency of aquaculture production is important for both economic and environmental sustainability. The purpose of this work was to define the relationships between feed intake, weight gain, and feed efficiency (measured as residual feed intake) in rainbow trout Oncorhynchus mykiss fed either to apparent satiation or a limited ration. The results indicated that under an apparent satiation feeding regime, a weak but significant correlation existed between weight gain and residual feed intake (RFI; r = −0.31, P < 0.04). When fed a limited ration, the correlation between weight gain and RFI was stronger (r = −0.57, P < 0.001). Genetic differences between family groups were detected only under the apparent satiation feeding regime and not under limited feeding. Although these experiments were conducted on different groups of fish, it appears that the variation in RFI was greater in satiation-fed fish than in fish fed a limited ration (coefficient of variation = 174% versus 33%). Estim...

Relationship of Gonadal Development to Body Size and Plasma Sex Hormone Concentrations in Female Channel Catfish

Abstract Most channel catfish Ictalurus punctatus do not spawn until age 3, which makes the process of genetic selection for desired characteristics time consuming. A simple method for identifying earlier-maturing fish would speed up the selection process. Two- and three-year-old females (U.S. Department of Agriculture [USDA]-103 strain) were used to correlate body weight and plasma sex hormone concentrations with gonadal development. We also examined the potential of reducing the time to maturation with exogenous estrogen. The USDA-103 females are known to spawn at age 2 in a higher percentage than other strains. The body weight of 2-year-old USDA-103 females ranged from 436 to 884 g, and the gonadosomatic index (GSI) ranged from 0.34% to 6.64%. A population of 2-year-old USDA-103 fish that had been hormonally sex-reversed to females (SR103) weighed from 400 to 1,400 g and had GSIs ranging from 1% to 10%. Three-year-old SR103 females weighed from 1,300 to 2,800 g and had GSIs ranging from 2% to 14%. Only...