Submitted to: Aquaculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/25/2013
Publication Date: 12/12/2013
Citation: Deng, D., Ju, Z., Dominy, W., Conquest, L., Smiley, S., Bechtel, P.J. 2013. Effect of replacing dietary menhaden oil with pollock or soybean oil on muscle fatty acid composition and growth performance of juvenile pacific threadfin (polyactylus sexfilis). Aquaculture. 423:91-97. Interpretive Summary: Fish oil normally contains high levels of long-chain polyunsaturated fatty acids (LC-PUFA), which is important for supporting the optimal growth and normal health of fish. Carnivorous marine fish are being fed with feeds formulated with fish oil as a major lipid source. There will not be sufficient fish oil to meet the increasing demand of aquaculture in the near future, therefore, it is important to explore different sources of fish oil, or to investigate alternative oils to substitute fish oils in aquatic feeds. Fish oil is used as a major lipid source in a commercial feed that is being fed to moi (Pacific threadfin). No study has been conducted to investigate the potential of this fish in utilization of vegetable oil as a lipid source. Also, pollock oil as a new potential fish oil has never been evaluated in this species of fish. The objective of this study was to compare the nutritional value of pollock oil and menhaden oil; and to evaluate the potential of soybean oil to replace the pollock oil in a feed for moi. This study compared the nutritional values of menhaden fish oil and pollock oil, and studied the potential of replacing dietary pollock oil by soybean oil based on the effect of pollock oil on growth performance, body composition, and muscle fatty acid profiles of juvenile moi. All test diets contained 42% crude protein and 12% crude lipid, with 8% added fish oil (menhaden or pollock oil) or dietary replacement of pollock oil by soybean oil (0, 25, 50, 75 or 100%). Pacific threadfin were hand fed these diets at 4-6% body weight daily for 8 weeks with 3 replications per dietary treatment. Results of this study suggested that the complete replacement of added fish oil with soybean oil had no detrimental effect on the growth of juvenile moi when 40% fishmeal was formulated in a diet. Also, pollock oil could replace menhaden oil in feed for moi without affecting growth performance and nutritional quality of whole fish or their muscle. The replacement of added pollock oil by soybean oil had no detrimental effects on the growth performance of juvenile moi, however, it depleted the level of n-3 LC-PUFA in the muscle of fish under current test conditions. These results are useful in developing a cost effective dietary formulation for aquaculture of moi. A longer term study over the entire production cycle of moi is recommended to confirm the application of our finding to commercial production.
Technical Abstract: This study compared the nutritional values of menhaden fish oil and pollock oil; and studied the potential of replacing dietary pollock oil by soybean oil based on the effect of pollock oil on growth performance, body composition, and muscle fatty acid profiles of juvenile Pacific threadfin. All test diets contained 42% crude protein and 12% crude lipid, with 8% added fish oil (menhaden or pollock oil) or dietary replacement of pollock oil by soybean oil (0, 25, 50, 75 or 100%). Pacific threadfin (initial body weight, 18.6 g) were hand fed these diets at 4-6% body weight daily for 8 weeks, with 3 replications per dietary treatment and 15 fish per replicate. Fish were cultured in an indoor flow-through system with 31‰ salinity seawater at 26°C. Growth performance, proximate composition of whole body, and muscle were similar among different dietary treatments (P>0.05). In contrast, fish fed the diet containing 8% soybean oil exhibited a significantly higher level of lipid in the liver than fish fed the diet with 8% pollock oil. Fatty acid profiles in muscle reflected the profiles of dietary fatty acid, with a decreased level of n-3 long chain polyunsaturated fatty acid (n-3 LC-PUFA) and increased levels of C18:2n-6 and C18:3n-3 in fish fed the soybean oil diet. Results of this study suggested that the complete replacement of added fish oil with soybean oil had no detrimental effect on the growth of juvenile Pacific threadfin when 40% fishmeal was formulated in a diet under current test conditions. A diet with 40% fishmeal might have provided sufficient essential fatty acids to support the normal growth of this fish. This result is useful in formulating an optimal diet to reduce feed cost in Pacific threadfin farming. However, a longer term study is needed to investigate whether changes in the fatty acid compositions of fish muscle may influence the market value of these fish and a feeding strategy of using “finishing diet” may be necessary to restore fatty acid profiles of these fish before they are marketed.