Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2007
Publication Date: 12/1/2007
Citation: Aksoy, M., Shelby, R.A., Lim, C.E., Klesius, P.H. 2007. Growth performance, and proximate and fatty acid composition of channel catfish, Ictalurus punctatus, fed for different duration with a commercial diet supplemented with various levels of menhaden fish oil. Journal of the World Aquaculture Society. 38(4): 461-474. Interpretive Summary: There is evidence that high levels of n-3 highly unsaturated fatty acids (n-3 HUFA) in marine fish oil play vital roles in human nutrition, disease prevention and health promotion. Freshwater fish, including channel catfish, contain low levels of these fatty acids (FA) but high levels of n-6 FA. However, it has been shown that fatty acid composition of fat in fish tissues is influenced by dietary fatty acid composition. Channel catfish fed diets supplemented with fish oil had significantly increased concentrations of n-3 HUFA and the tissue concentrations of n-3 HUFA are affected by dietary levels of fish oil. However, there is no published information on the effect of feeding duration and dietary fish oil levels on the accumulation of these fatty acids in fish tissues. Thus, this study was conducted to evaluate the effect of feeding duration of diets supplemented with various levels of fish oil on n-3 HUFA content in channel catfish fillets. Growth, feed utilization, and whole body proximate and fatty acid composition of fish receiving various dietary levels of fish oil for 15 weeks were also determined. Results of this study indicate that supplementation of menhaden fish oil at levels up to 9% to a commercial catfish diet had no effect on growth, feed intake and utilization efficiency, and survival of juvenile channel catfish reared under laboratory conditions. Increasing supplemental fish oil levels increased tissue lipid and decreased moisture and protein contents. Tissue FA contents, particularly n-3 and n-3 HUFA, and the ratio of n-3/n-6 FA increased with increasing dietary fish oil levels. Feeding juvenile channel catfish the 6% added fish oil diet for 6 weeks appeared to be sufficient to maintain desirable n-3/n-6 FA ratios and n-3 HUFA levels. However, maximum n-3 FA (in mg/g fillet) was obtained in fish fed the highest (9%) fish oil diet for 15 weeks. Although increasing levels of n-3 FA in catfish fillets can be accomplished by feeding diets supplemented with menhaden fish oil at various time periods, feeding high levels of fish oil diets have been reported to impart objectionable fishy flavor (Morris et al. 1995). Thus, it is suggested that the maximum amount of n-3 FA in fillets that do not adversely affect flavor and is acceptable by consumers as a means to reduce the risk of cardiovascular disease should be established prior to feeding fish diets containing high levels of n-3 HUFA.
Technical Abstract: This study was conducted to evaluate the effect of supplemental menhaden fish oil at levels of 0, 3, 6 and 9% to a commercial diet and feeding duration on growth performance, proximate body and tissue fatty acid (FA) composition of juvenile channel catfish, Ictalurus punctatus. Each diet was fed to juvenile catfish (mean weight 14.6 g) in four random aquaria to apparent satiation twice daily for 15 weeks. Boneless, skinless fillets from three fish/tank at weeks 3, 6, 9, 12 and 15, four whole fish at week 15, and 15 initial fish (week 0) were collected for their proximate composition and fatty acid composition. Levels of dietary fish oil did not significantly influence final weight gain, feed intake, feed efficiency ratio and survival of channel catfish. Whole body and fillet lipid contents were directly correlated to the dietary lipid levels, while moisture contents were inversely related to dietary lipid levels. Protein contents of both whole body and fillet of fish fed 6% or 9% fish oil diets were significantly lower than that of the control. Fillet moisture contents progressively decreased whereas fillet lipid increased with increasing feeding duration. Fillet protein and ash contents significantly increased up to weeks 6 and 9, respectively. No further increase in the values of these parameters was observed beyond these periods. Whole-body and fillet FA composition was influenced by dietary FA composition. Significant increase in saturated and total n-3 fatty acids, and decrease in monoenoic and total n-6 FA in whole-body and fillet were observed at each incremental level of dietary fish oil. Fish fed the 9% fish oil diet had the highest level of total n-3, n-3 highly unsaturated fatty acids (n-3 HUFA) (includes C20 members of the n-3 family), and ratio of n-3 to n-6 FA in all tested tissues. Percentages of n-3 and n-3 HUFA in fillet of fish fed the control and 3% fish oil diets decreased with increasing feeding periods, whereas those of fish fed 6 or 9% added fish oil diets remained stable or increased. Ratios of n-3/n-6 were statistically comparable throughout the 15-week feeding, although the values at weeks 9, 12 and 15 were numerically lower than that at week 6. When expressed in terms of mg/g fillet, the highest concentration of n-3 was obtained in fillets of fish fed the 9% added fish oil diet for 15 weeks.