Influence and the underlying mechanisms of substrate type on the growth of razor clam Sinonovacula constricta

The bivalve aquaculture sector constitutes a vital pillar of China's fisheries economy, with substrate serving as a pivotal environmental determinant influencing the efficacy of aquaculture practices. However, how substrate characteristics affect the bivalve growth remains unclear. In the present study, the widely cultured bivalve species, namely the razor clam Sinonovacula constricta, was chosen as the subject of our research, and an experiment was conducted to examine its cultivation across four distinct types of substrates: artificial, sandy, muddy, and sandy silt substrates. The results demonstrated that substrate grain size (GS) was a pivotal determinant influencing the growth of razor clams. Growth indicators, including wet weight, shell length, shell width, exhibited a significant decrease as the substrate grain size increased. More specifically, S. constricta exhibited optimal growth within the GS range of 6.7–16.0 μm and the most inferior growth at a substrate grain size of 293.0 μm. A coarse-grained substrate (293.0 μm) significantly impeded essential behaviors such as burrowing and feeding, thereby markedly reducing the growth rate of razor clams. Furthermore, extended exposure to a coarse-grained substrate may trigger oxidative stress in S. constricta, leading to cellular structural and functional impairments, which subsequently suppress the activity of antioxidant enzymes (e.g., catalase) and downregulate the expression of antioxidant genes (e.g., catalase, superoxide dismutase, glutathione peroxidase). Despite the substrate significantly altering the phosphorus concentration in the overlying water, the frequent water exchanges within the aquaculture system prevented the conversion of these elevated phosphorus levels into accessible primary productivity for filter-feeding razor clams, thus yielding no significant impact on clam growth. These findings provide valuable insights for substrate selection in razor clam aquaculture, thereby contributing to the enhancement of both the quality and economic viability of razor clam farming operations.