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

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., ۵.۹۲, ۱۰.۰۸, ۱۱.۶۶, and ۱۴.۵۳) on the emerging larvae foregut development of rainbow trout was examined. Larvae samples were taken from day ۲۲ to ۳۶ 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 ۳۶ post fertilization in larvae hatched from eggs with DHA:EPA ratios of ۱۴.۵۳ and ۱۰.۰۸. The highest and lowest intestinal folds height were also observed in larvae hatched from eggs with DHA:EPA ratios of ۱۰.۰۸ and ۱۴.۵۳, respectively. The mucosal-submucosa layer thickness was the highest in larvae hatched from eggs with DHA:EPA ratio of ۱۰.۰۸. Enterocyte’s count was the highest in larvae obtained from eggs with DHA:EPA ratio of ۱۰.۰۸ on day ۳۶ post-fertilization. The highest and lowest number of goblet cells were enumerated in larvae obtained from eggs with DHA:EPA ratios of ۵.۵۳ and ۱۴.۵۳, 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 ۰.۲۸ could result in the egg with DHA:EPA ratio of ۱۰.۰۸ which in turn yielded larvae with better foregut development parameters compared to those larvae emerged from the eggs with increased DHA :EPA ratio.

Keywords:

Digestive tract , Docosahexaenoic acid , Eicosapentaenoic Acid , Rainbow trout