Effects of feeding level and sexual maturation on carcass and fillet characteristics and indices of protein degradation in rainbow trout (Oncorhynchus mykiss)

Authors: Cleveland, Beth; KENNEY, P. BRETT - West Virginia University; MANOR, MEGHAN - West Virginia University; Weber, Gregory - Greg

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2012
Publication Date: 2/12/2012
Citation: Cleveland, B.M., Kenney, P., Manor, M.L., Weber, G.M. 2012. Effects of feeding level and sexual maturation on carcass and fillet characteristics and indices of protein degradation in rainbow trout (Oncorhynchus mykiss). Aquaculture. 338-341:228-236.

Interpretive Summary: Comparisons between maturing diploid and sterile triploid rainbow trout presents a unique model with which to charactize the physiological effects of maturation in fish. Muscle degradation is known to occur in sexually maturing trout, but it is unclear if increasing feed intake alleviates effects of maturation on muscle protein loss. Our evidence indicates an up-regulation in muscle protein degradation in maturing trout, but not in sterile triploid trout, across multiple ration levels. A net loss of muscle protein occurred only during severe nutrient restriction, indicating that adequate levels of feed intake enables replacement of the degraded proteins. While feeding to satiation reduces feed efficiency, severe nutrient restriction reduces egg size and causes muscle loss, both with negative impacts on reproductions efficiency and profitability. Therefore, moderate feed restriction may be an optimal feeding strategy for fish that are retained for additional breeding cycles.

Technical Abstract: Sexual maturation in many species of fish including salmonids requires mobilization of energy and nutrient resources to support gonad growth. During sexual maturation, particularly vitellogenesis, proteins are mobilized from muscle tissue, which is evidenced by increased expression of proteolytic genes and decreased muscle protein content. However, it is unknown how ration level affects the proteolytic response in skeletal muscle during sexual maturation. In the current study, sexually maturing female diploid rainbow trout (Oncorhynchus mykiss) were fed at 0.25% and 0.50% tank weight, and satiation, for twelve weeks approaching ovulation. Triploid female trout, which do not develop gonads, were included at the 0.50% ration level. Over the study period, gonad somatic index (GSI) increased in sexually mature diploids from 3.98% to approximately 13% and was unaffected by ration. Reduced feed intake and maturation negatively affected protein and lipid deposition in skeletal muscle, as indicated by reduced fillet weight and reduced fillet protein and lipid content. During mid-vitellogenesis, proteolytic gene expression was higher in diploids compared to triploids and the majority of the differentially expressed genes were cathepsin and autophagy-related genes. These differences increased with maturation and expanded to include multiple components of the proteasome, ubiquitin ligases, calpastatins, and caspase 9. Expression patterns of multiple proteolytic genes suggests fish consuming the 0.25% and satiation rations had greater capacities for protein degradation than fish fed the moderate 0.50% ration. In summary, these results suggest that maturation increases protein degradation and that maximum levels of feed intake do not reduce the rate of protein mobilization from skeletal muscle. However, higher levels of feed intake prevent a net loss of muscle protein, suggesting that dietary nutrients are able to replace endogenous nutrients mobilized from skeletal muscle in support of gonad growth.