Z.O. Merican, K.F. Shim-1997
Aquaculture, 157: 277-295
Abstract:
The nutrient requirement levels of linolenic (18:3n-3) and docosahexaenoic (22:6n-3) acids for juvenile Penaeus monodon were investigated. Shrimp were fed semipurified diets containing different levels of 18:3n-3 (0.5, 1.0, 1.5, 2.0, 2.5 and 3.0%) and 22:6n-3 at 0.12, 0.25, 0.5, 1.0, 1.5 and 2.0% in the dry diet. The lipid mixture in the control/conditioning diet contained 5% of equal proportions of 16:0 and 18:1n-9. In the reference diet, the dietary lipid was refined cod liver oil. Each diet was fed to five replicate groups of 20 shrimp (mean initial weight, 73 +/- 12.1 mg). Shrimp were fed the conditioning diet for seven days prior to feeding the treatment diets. Using the broken line analysis, the optimal requirement levels of 18:3n-3 and 22:6n-3 were determined to be 2.50% and 1.44%, respectively. The estimated requirements for 18:3n-3 and 22:6n-3 based upon other quantitative analysis or other responses were quite similar. Growth was significantly (P<0.05) lower in shrimp fed 3.0% dietary 18:3n-3 as compared to those fed 2.50% dietary 18:3n-3. Growth response was significantly (P<0.05) improved with a supplementation of 22:6n-3 into diets at 0.12%. Increases in the level of supplementation of 22:6n-3 beyond the optimum requirement level, did not result in any significant (P>0.05) increases in weight gain. Survival responses were greater with a lower supplementation level of 22:6n-3 relative to 18:3n-3. Tissue fatty acid analysis showed that the content of 18:3n-3 and 22:6n-3 closely reflected dietary levels, particularly in the midgut gland. The level of incorporation of dietary 18:3n-3 and 22:6n-3 into the polar lipids of the midgut gland was shown as a good method to estimate requirement levels. No significant (P<0.05) changes in 20:5n-3 and 22:6n-3 in tail muscle lipids of shrimp fed dietary 18:3n-3 indicated no apparent bioconversion of 18:3n-3 to higher n-3 polyunsaturated fatty acids. However, concomitant increases in tissue content of 20:5n-3 in shrimp fed increasing dietary levels of 22:6n-3 suggested a retroconversion of 22:6n-3 to 20:5n-3. This confirmed the results of an earlier investigation concerning the relationship between levels of dietary HUFA.
(School of Biological Sciences, National University of Singapore, Kent Ridge 119260, Singapore)