Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: February 15, 2009
Publication Date: February 15, 2009
Citation: Cleveland, B.M., Weber, G.M., Silverstein, J. 2009. Mechanisms contributing to family variations in feed conversion and growth in rainbow trout (Oncorhynchus mykiss). Aquaculture America Conference. Technical Abstract: Feed costs often represent greater than 50% of the operating expenses in aquaculture production. Therefore, the efficiency at which fish convert feed into biomass directly impacts the profitability of a farm. Understanding the physiological and genetic mechanisms contributing to family variations in feed efficiency will enhance how we use genetic selection to improve feed conversion in rainbow trout. The rate of protein turnover is a mechanism that affects nutrient retention and, consequently, the conversion of feed into biomass. This study investigates how indices of protein degradation correlate to family variations in feed conversion and growth. Yearling fish (n=7) from each of eight families were individually stocked into 6- or 9-L tanks in a closed recirculation system. Water was exchanged twice daily and ammonia, nitrite, and nitrate levels were monitored twice weekly. On day 1 of the feeding trial fish weights were recorded and for five weeks fish were fed twice daily to satiation. Final weights and total feed consumption were determined at the conclusion of the trial. Also on day 1, 14 fish from each family were harvested from 7 30-gallon tanks (n=2 fish/family/tank). One fish per family was kept whole for proximate analysis while liver and white muscle samples were removed from the remaining fish and snap frozen for gene expression analysis. Family feed conversion ratio was correlated with the mRNA abundance of several proteolytic transcripts in both liver and muscle. The mRNA abundance of the ubiquitin ligase, MAFbx, was positively correlated with feed conversion ratio (g fed/g gain) in both liver (P=0.0092) and white muscle (P=0.03) and negatively correlated with body weight in liver (P=0.04). These data suggest that variations in regulation of the ubiquitin-proteosome pathway can impact feed efficiency and growth. Additionally, there was a positive trend between liver cathepsin L (P=0.060) and caspase 3 (P=0.058) mRNA abundance and family feed conversion, indicating that these proteolytic pathways can also impact performance. A significant family effect (P<0.05) on expression of numerous proteolytic genes was observed in liver, but not white muscle. Together, these results suggest that mechanisms affecting differential rates of protein degradation contribute to family variations in feed conversion.