Screening the biochemical composition of some marine microalgal species for feeding Cyclops abyssorum divergens

Recently, the use of microalgal bioproducts in aquaculture research has gotten consideration. The current study aims to screen the biochemical components of three microalgae: Nannochloropsis salina, Chlorella salina and Tetraselmis chuii for using in the feeding of Cyclops abyssorum divergens copepods that are suitable prey for the mouth gape of the cultured fish larvae. The effect of different initial densities of these algal cells used for copepods feeding was determined by estimation of proximate composition, polyunsaturated fatty acids (PUFAs), amino acids (AAs) and enzyme activities of copepods. N. salina showed high protein and lipid contents, while C. salina presented high carbohydrate content. C. salina and T. chuii presented high PUFAs, with proportions of 22.35 and 22.67%, respectively, and are considered as the source of n-3 fatty acids. Also, they had higher concentrations of total AAs (21.46 and 24.14 mg. g−1 dry wt., respectively). The experiment study showed that the C. salina diet at an initial concentration of 1 × 106 cells ml−1 resulted in a maximum increase of copepods population density (503.3%) and high protease and trypsin activities (42.65 and 31.80 U. mg−1 protein, respectively) in copepods. T. chuii diet at an initial concentration of 1 × 106 cells ml−1 resulted in a maximum protein, lipid, PUFAs and AAs contents of copepods. Therefore, C. abyssorum divergens copepods after 18 days feeding with an initial concentration of 1 × 106 C. salina or T. chuii cells ml−1 are the suitable candidate diets in larviculture because they achieved higher productivity and attained better nutritional composition of the copepods.