Ammonia nitrogen is a common toxic substance in the aquatic system, which seriously threatens the survival and growth of clams. However, less is known about the ammonia metabolism and detoxification strategy in razor clam. In this study, the polymorphism of the Glutamine synthetase gene from Sinonovacula constricta (Sc-GS) was found to be related to ammonia tolerance. By comparing the coding sequence (CDS) region of Sc-GS from two geographical populations, a total of 14 and 12 single nucleotide polymorphisms (SNPs) were identified, respectively, of which 10 loci were shared between the two populations. Among them, the locus c.1133T > G exhibited an extremely significant and strong association with ammonia tolerance in both populations (P < 0.01), and it was missense mutation, which led to the amino acid change from leucine (Leu) to arginine (Arg). Furthermore, the results about H&E staining and immunohistochemistry of Sc-GS protein in gills and hepatopancreas revealed that it was specifically localized in the lateral cilia of gill filaments and the endothelial cells of hepatocytes. After inhibiting the Sc-GS expression by RNA interference (RNAi) technology, the transcript levels of Sc-GS were extremely significantly downregulated at 24, 48, 72, and 96 h (P < 0.01) in the hepatopancreas. Taken together, these results indicated that the Sc-GS gene may participate in ammonia metabolism. In addition, these results will help to demonstrate the role of Sc-GS in ammonia nitrogen metabolism and provide markers related to ammonia nitrogen tolerance for molecular marker-assisted selection (MAS) of the razor clam.

Excessive ammonia accumulation poses a significant threat to aquatic species. Potamocorbula ustulata, known for its burrowing behavior and high population density, may experience elevated ammonia levels in its environment. However, its ammonia stress response mechanisms remain unclear. This study investigates the physiological and molecular responses of P. ustulata to acute ammonia exposure. Antioxidant enzyme activity was significantly altered in the gills and hepatopancreas, with GS, GDH, and ARG levels markedly increasing in the hepatopancreas. Transcriptome analysis revealed that after 24 h of exposure, differentially expressed genes (DEGs) were enriched in apoptosis and inflammation-related pathways (MAPK, NF-kB, NOD-like receptor signaling). By 96 h, DEGs in the gills were associated with nitrogen metabolism and transport, while those in the hepatopancreas were linked to oxidative phosphorylation and amino acid metabolism. Key ammonia transport and excretion genes, including V-type H⁺-ATPase, Ammonium transporter Rh, and Na⁺/K⁺-ATPase, were significantly upregulated in the gills, while glutamine synthetase and glutamate dehydrogenase were upregulated in the hepatopancreas (p < 0.05). These findings suggest that ammonia stress disrupts antioxidant defense, triggers inflammation and apoptosis, and enhances ammonia tolerance through excretion, glutamine conversion, and urea synthesis. This study provides insights into the molecular mechanisms underlying ammonia tolerance in bivalves.

This study investigated the effects of culture density on the phytoplankton communities in an integrated culture model of the blood clam Tegillarca granosa and Pacific white shrimp Litopenaeus vannamei. Two treatments were set up: L (L. vannamei 18 ind/m², T. granosa 33 ind/m²) and H (L. vannamei 36 ind/m², T. granosa 66 ind/m²). The management methods were the same during the experimental period, and the feed intake was determined according to L. vannamei. The results showed that there were more than 38 species of phytoplankton in the ponds, belonging to six phyla and 28 genera; the diversity index of the phytoplankton was higher in the early stage of the experiment and lower in the later stage; the average biomass of phytoplankton was 21.74 × 10⁴ ind/L; and the culture density had no significant effect on water quality. This study showed that a reasonable increase in culture density would not cause significant adverse effects on the environment. It is possible to increase the stocking density of shrimp with the mollusk without causing inadequate conditions for the phytoplankton community and water quality.