Clam challenges high concentrations of algae diet environment: Growth performance, metabolism physiology, and related gene expression characteristics

Abstract

Increasing coastal pollution leads to frequent algal blooms, but little is known on the effect of growth and development in organisms with increasing algal concentration. In recent years, the clam Cyclina sinensis has been an important marine economic shellfish that is widely cultivated. This study investigated the effects of different Chlorella concentrations (5 × 105 cell/L (Diet T1), 1.25 × 106 cell/L (Diet T2), 1.3 × 107 cell/L (Diet T3), 1.25 × 108 cell/L (Diet T4), and 1.5 × 109 cell/L (Diet T5)) on the growth, enzyme activities of digestive, immune, and respiratory metabolism, and hepatopancreatic transcriptome gene expression characteristic response of C. sinensis. Results showed that the shell length growth rate, shell height growth rate, and survival rate of C. sinensis significantly decreased as the Chlorella concentration reached 5 × 105 cell/L. The condition factor of C. sinensis in Diet T1 and the hepatopancreas index of C. sinensis in Diet T4 were significantly higher than those in the other groups (P < 0.05). The enzyme activities of superoxide dismutase increased significantly with the rise in concentration of Chlorella, but the highest lysozyme in the hepatopancreas of C. sinensis was observed in the Diet T1 group. The enzyme activities of acid phosphatase and amylase in Diet T3, trypsin in Diet T5, lipase and succinate dehydrogenase in Diet T4, and lactate dehydrogenase in Diet T1 of C. sinensis were significantly higher than those in the other groups (P < 0.05). These results suggest that some enzyme activities related to digestion, metabolism, and respiration are inhibited with the Chlorella concentration increased. Furthermore, transcriptome results showed that the expression levels of G6P, IGFBP, CHI3L1, FAS, MyHC, and other genes related to glucose, protein, and fatty acid metabolism of C. sinensis were significantly downregulated in the Diet T3 and Diet T5 groups. All these results suggest that Chlorella concentrations above 5 × 105 cell/L should be avoided in practice. This study provides a scientific basis for C. sinensis culture and further extends the understanding of the metabolism of bivalves with diet concentration.