Assessment of the fecundity, population growth and fatty acid composition of Apocyclops royi (Cyclopoida, Copepoda) fed on different microalgal diets

The brackish cyclopoid copepod Apocyclops royi is used in Taiwanese aquaculture industry as a prey for fish larvae. This study investigated the effects of seven microalgal diets, namely single-species diets of Isochrysis galbana (ISO), Nannochloropsis oculata (NAN), and Tetraselmis chui (TET), two-species diets (ISO+NAN, ISO+TET and TET+NAN), and a three-species diet (ISO+NAN+TET), on the population growth, female fecundity and fatty acid composition of A. royi. For reproductive traits, the combination ISO+NAN was found to be the most supportive diet for both population growth and female fecundity. For nutritional value, copepods fed ISO and ISO+NAN were detected to have the highest content of docosahexaenoic acid (DHA) (18.99% and 10.73% total fatty acid, respectively) and, more importantly, a high DHA/EPA ratio (6.09 and 4.09, respectively). Additionally, a comparison of fatty acid composition between copepods and microalgae gives a tentative indication that A. royi may have the ability to synthesize long-chain polyunsaturated fatty acids (PUFA) from short-chain PUFA. Our findings illustrate that ISO+NAN is the most suitable microalgal diet for mass culturing A. royi because it increases productivity and enhances the nutritional value of the copepods for use as fish larvae prey.