The effects of 3 different microalgae species on the growth, metamorphosis and MYP gene expression of two sea urchins, Strongylocentrotus intermedius and S. nudus

As a result of the increase in demand for sea urchin gonads, which are considered a gourmet food, the sea urchin aquaculture industry has gradually expanded in some South American and Asian countries. This study investigated the growth, metamorphosis and MYP gene expression of larvae of two species of sea urchin (Strongylocentrotus intermedius and Strongylocentrotus nudus) fed with four microalgal diets: Chaetoceros muelleri, Dunaliella tertiolecta, Isochrysis galbana, and a mixture of the three. The larvae fed the C. muelleri and mixture diets were successfully raised to competence for metamorphosis and showed better stomach growth, development rates and metamorphosis rates than the larvae that were fed D. tertiolecta or I. galbana. The results also suggest that the larvae could accumulate long-chain polyunsaturated fatty acids (LC-PUFAs), such as docosahexaenoate (DHA; 22:6n-3), eicosapentaenoate (EPA; 20:5n-3) and arachidonate (ARA; 20:4n-6), either by the assimilation and retention of dietary fatty acids or by synthesis from a-linolenic acid (18:3n-3) and linoleic acid (18:2n-6). Moreover, an accumulation of n-6 and n-3 LC-PUFAs and higher ARA/EPA ratios in the larvae appeared to be associated with improved larval performance. The results also showed that the MYP gene expression levels in the larvae fed the C. muelleri and mixed diets were significantly higher than in the D. tertiolecta and I. galbana groups. In addition, the trend of the MYP gene expression in the different stages was 6-arm stage > 8-arm stage > 4-arm stage > fertilized eggs > prismatic stage. These results provide suggestions for diet selection for sea urchin larvae and the fatty acid composition of diets for urchin larvae, and they provide a reference for further study of the effects of diets on the gene expression of MYP in larvae.