Liver transcriptome analysis reveals the molecular responses to low-salinity in large yellow croaker Larimichthys crocea

Abstract The large yellow croaker Larimichthys crocea is a euryhaline marine fish with wide consumptions and high commercial values in China. Low-salinity culture of L. crocea has been proposed to suppress the pathogens with low cost. However, the responses of L. crocea at molecular level to low salinity have not been fully understood. In this study, Illumina RNA-seq gene expression system was applied to globally screen the genes and pathways involved in the responses in liver tissues of L. crocea to low-salinity conditions. Compared with the control (24 ppt), a total of 1369, 685, 2980 and 3469 differentially expressed genes (DEGs) were identified in low-salinity treatments (8, 6, 4 and 2 ppt) for 40 days, respectively. Among them, 164 DEGs were common in 4 low-salinity groups. According to the KEGG pathway analysis, the DEGs were involved in material metabolism (carbohydrate, protein, and lipid metabolism), energy metabolism, growth, immune system, signal transduction, transcription and translation, and apoptosis. With respect to metabolism, up-regulated oxidative phosphorylation was the primary enriched pathways in response to low salinities of 6 ppt (S6) and 4 ppt (S4). The salinities of 8 ppt (S8) and 2 ppt (S2) were characterized by enhanced anabolism and inhibited material and energy metabolism, respectively. Concerning immune responses, innate immunity was promoted in S6 and S4 groups as a general stress response. L. crocea cultured in S4 group suffered few immune and inflammation risks, indicated by the negative responses to CD209 antigen (CD209) and C-reactive protein (crp). Moreover, low salinities induced higher absolute weight gain rate (AWGR) and survival rate of L. crocea, and S4 group presented the highest AWGR and survival rate. Our findings indicated that salinity of 4 ppt was preferable for the low-salinity farming of L. crocea. Overall, this work provides new insights into the molecular responses of L. crocea to low-salinity and references for L. crocea culture in low salinities.