February 15-18, 2009 Washington State Convention Center Seattle ...

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MECHANISMS CONTRIBUTING TO FAMILY VARIATIONS IN FEED CONVERSION AND
GROWTH IN RAINBOW TROUT (Oncorhynchus mykiss)
Beth M. Cleveland*, Gregory M. Weber and Jeffrey T. Silverstein
National Center for Cool and Cold Water Aquaculture
ARS-USDA
11861 Leetown Rd.
Kearneysville, WV 25430 USA
beth.cleveland@ars.usda.gov
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 30gallon
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