is eicosapentaenoic acid (epa) essential for juvenile
grouper (Epinephelus malabaricus)?
F.C.
Wu, H.Y. Chen
Eicosapentaenoic
acid (20:5n3; EPA) has been known to play an essential role in the fatty
acid nutrition of many freshwater and marine finfish. Our studies with the
warm water grouper, however, show the limited role of dietary EPA in
affecting fish growth and immune responses. When juvenile grouper were given
a series of experimental diets with different ratios of DHA (22:6n3) and
EPA, the group that fed on the diet with higher DHA:EPA ratio showed better
growth and immune responses. Analysis of body fatty acid composition
indicates that grouper has limited ability to convert EPA to DHA. A second
study in which juvenile grouper were fed with diets that differ in ratios of
linolenic acid (18:3n3; LNA) and linoleic acid (182n6; LA) shows that higher
LNA:LA ratio resulted in better fish growth and immune responses. Dietary
inclusion of LNA clearly increased the presence of tissue n-3
polyunsaturated fatty acids, implicating the conversion of LNA to EPA. It is
thus prudent to suggest that dietary EPA is not essential if LNA is
adequately supplemented. The need of grouper for highly unsaturated fatty
acids is better satisfied with DHA than with EPA because of the limited
ability to convert EPA to DHA.
(Institute
of Marine Biology, National Sun Yat-sen University, Kaohsiung 80424 Taiwan)