Effect of various dietary levels of highly unsaturated fatty acids and polyunsaturated fatty acids on some morphometric features of duodenum in newly weaned rainbow trout (Oncorhynchus mykiss) larvae

The present study was to investigate the effect of various dietary levels of unsaturated fatty acids (HUFA and PUFA) on some morphometric features of duodenum in newly weaned rainbow trout larvae. Therefore, eight different experimental diets consisted of various dietary levels of HUFA (0, 0.5, 1 and 2 percent) at a fixed dietary PUFA of 20 percent (the first experiment) and various dietary PUFA levels (10, 20, 30 and 40 percent) at a fixed dietary HUFA of 8 percent (the second experiment) were formulated. Stocking density of larvae was 100 larvae per each container and the experiments lasted for six weeks. At the end of the experiments, six fish were randomly taken and the proximal intestine was dissected out and fixed for classical histological studies. In the first experiment concomitant with any increase in dietary HUFA content, epithelial thickness and villous height significantly decreased (P<0.05) and according to the results the appropriate HUFA level could be 0.5 percent of the dietary lipid moiety. However, in the second experiment only villous height of duodenum was affected by experimental diets (P<0.05) and villous height was the highest (207.2±10.3μm) at PUFA level of 20 percent of the total dietary lipid. In conclusion, it is recommended that in the case of using vegetable oils in feed formulation (to replace marine lipid sources) led to higher PUFA levels, dietary HUFA levels could be increased to eight percent for keeping normal intestine morphometry.