Investigating the effects of different DHA/EPA ratios in rainbow trout (Oncorhynchus mykiss) egg composition on foregut development of larvae.

Abstract

Lecithotrophic larvae utilize extensive yolk reserves for early development. In this study, the effect of egg docosahexaenoic acid (DHA):eicosapentaenoic acid (EPA) ratios (i.e., 5.92, 10.08, 11.66, and 14.53) on the emerging larvae foregut development of rainbow trout was examined. Larvae samples were taken from day 22 to 36 post-fertilization. Thin whole body longitudinal sections were prepared and stained by Hematoxylin and Eosin and Alcian blue procedure. The sections were examined regarding epithelial layer thickness, intestinal fold height and mucosal layer thickness along with number of enterocytes and goblet cells. Results indicated that maximum thickness of the epithelium was observed on day 36 post fertilization in larvae hatched from eggs with DHA:EPA ratios of 14.53 and 10.08. The highest and lowest intestinal folds height were also observed in larvae hatched from eggs with DHA:EPA ratios of 10.08 and 14.53, respectively. The mucosal-submucosa layer thickness was the highest in larvae hatched from eggs with DHA:EPA ratio of 10.08. Enterocyte's count was the highest in larvae obtained from eggs with DHA:EPA ratio of 10.08 on day 36 post-fertilization. The highest and lowest number of goblet cells were enumerated in larvae obtained from eggs with DHA:EPA ratios of 5.53 and 14.53, respectively. In conclusion, our results revealed that feeding rainbow trout broodstock with diet contained highly unsaturated fatty acids (HUFA):polyunsaturated fatty acids (PUFA) ratio of 0.28 could result in the egg with DHA:EPA ratio of 10.08 which in turn yielded larvae with better foregut development parameters compared to those larvae emerged from the eggs with increased DHA :EPA ratio.