| Summary: | 碩士 === 國立中山大學 === 海洋生物研究所 === 96 === This research examined the quantitative effects of dietary conjugated linoleic acid (CLA) on juvenile cobia Rachycentron canadum with a mean initial weight of 10g and fed for 8 weeks. Four experimental diets that contained 16% crude lipid and 0%, 0.5%, 1.0% or 2.0% CLA were compared. At the end of the growth trial there was no significant differences in growth parameters. With increased CLA supplement, the body lipid content tended to reduce and protein content was significantly decreased. Increased dietary CLA caused significantly decreased hepatic FAS activity. Hepatic ME activity was decreased significantly in 0.5%, 0.75% and 1% CLA treatment, while no significant effect was detected on hepatic G6PDH activity. Total lipid contents of the liver and visceral fatty depot were significant decreased in 0.5%, 0.75% and 1% CLA treatment. There was a significant decrease in lipid content in the ventral muscle when CLA was supplemented at 0.75%, 1% and 2%. Fish fed 0.5% CLA had a lower adipocyte density in dorsal muscle, while fish fed 2% CLA treatment had a larger size of adipocytes in the liver and dorsal muscle. Gene expression of PPAR-α and PPAR-γ showed no definite trend. Significant deposition of CLA was found in the liver, ventral muscle, dorsal muscle and visceral fatty depot of the cobia. The deposition ratio of cis-9, trans-11 CLA was slightly higher than that of trans-10, cis-12 CLA. Dietary CLA also affected the deposition of other fatty acids. Increased dietary inclusion of CLA significantly increased the total percentages of saturated fatty acids (SFA) but significantly decreased polyunsaturated fatty acids (PUFA). However DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid) contents of the visceral fatty depot were significantly increased. In terms of immune response, dietary CLA had no effect on respiratory burst activities of head kidney phagocytes. Serum of fish fed 0.5% CLA had significantly increased lysozyme activities. In conclusion, dietary CLA affected the metabolism of lipid and fatty acid composition of cobia juveniles, and enhanced slightly immune responses. As CLA can deposit in the tissues of cobia, production of CLA-containing fish as a functional food is thus possible in cobia through dietary manipulation. An supplemental rate of 0.5% CLA is the optimal concentration considering fish nutrition and cost effectiveness.
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