Physiological response of the razor clam Sinonovacula constricta exposed to hyposalinity stress

Abstract

The razor clam Sinonovacula constricta is an economically important bivalve species in China, which inhabits the mudflat of intertidal and estuaries areas and frequently suffers the low salinity stress due to heavy rain events. The present study investigated the effects of hyposalinity stress (salinity 10, 5, 3, and 1) on osmoregulation and haemolymph microbiota in S. constricta after 7 days of exposure. The results showed that the survival rate of razor clams was only significantly reduced in the 1 ppt group compared to the control group (salinity 20) (P < 0.05). Haemolymph osmolality in razor clams reduced significantly with decreasing salinities (P < 0.05). Taurine, arginine, alanine and ornithine were the dominant free amino acids (FAAs) with higher contents in the haemolymph. Exposure to low salinities altered the composition of haemolymph FAAs, with alanine being the highest in the control group and taurine being the highest in the low salinity (LS) groups. Hyposalinity stress caused an increase in Na+/K+-ATPase (NKA) activity in gills, and histological analysis revealed severe hyperplasia in gills and a significant reduction in the length of gill filaments (P < 0.05). The microbial community variation in the haemolymph assessed by 16S rRNA sequencing explains that bacterial communities was shifted under low salinity stress. At the genus level, the relative abundance of Marinobacterium, Marinomonas and Pseudomonas changed significantly under hyposalinity stress (P < 0.05). These findings give further insight into the physiological responses and potential adaptation strategies of razor clams to hyposalinity stress and provide information for the development of inland low salinity culture.