High concentrations of ammonia nitrogen could result in the death of aquatic animals and cause a huge economic loss in the aquaculture industry. However, the metabolic responses to acute ammonia nitrogen stress remain largely unknown in Penaeus monodon. In this study, we first investigated the histological change in tissues in Penaeus monodon under 96 h acute ammonia nitrogen stress. The result of the paraffin section showed that acute ammonia nitrogen stress induced severe epithelial detachment and lumen dilatation of the hepatopancreas, swollen and hemocyte infiltration of the gills, and mucosa exfoliation and shortened villi of the intestine in Penaeus monodon, suggesting the impairment of the normal physiological function in these tissues. We next examined the change in the metabolic product in the plasma and the enzyme activity in the hepatopancreas after ammonia nitrogen stress. Upon ammonia stress, both the concentration of ammonia and urea nitrogen significantly increased, while there was no significant increase in the concentration of uric acid, which is consistent with the results that the enzyme activity of glutamine synthetase (GS), glutamate dehydrogenase (GDH), and aspartate transaminase (GOT) became significantly elevated and the enzyme activity of adenosine deaminase (ADA) in the purine metabolism pathway significantly decreased after ammonia stress, suggesting that shrimp could convert excessive ammonia to urea for ammonia detoxification through the ammonia–nitrogen metabolism pathways. Interestingly, we also observed a significant increase in superoxide dismutase (SOD) activity, suggesting a potential role of this antioxidant enzyme in the clearance of reactive oxygen species (ROS) induced via ammonia stress. Moreover, we found that acute ammonia nitrogen stress inhibited the enzyme activity of caspase 3 and caspase 8, suggesting an important role of apoptosis in protecting Penaeus monodon against acute ammonia stress. Overall, our findings revealed that Penaeus monodon may employ metabolic and purine pathways and undergo oxidative stress and apoptosis for ammonia detoxification under ammonia nitrogen stress, thus providing new insight into the metabolic response of shrimp to acute ammonia stress.

Stocking density plays an important role in P. monodon aquaculture. However, its underlying molecular mechanisms remain unknown. In this work, after a 40-day culture period, we studied the effects of different stocking densities (G1: 50, G2: 100, G3: 150 ind/m³) on P. monodon, assessing their growth performances, physiological indexes, and transcriptome profiles. It was found that increased stocking density greatly decreased the growth performance and survival rate as well as the level of immune enzymes (alkaline phosphatase, acid phosphatase) and antioxidant component (total antioxidant capacity, superoxide dismutase, reduced glutathione) activities. Transcriptomic analysis showed that there are 2284 differentially expressed genes in all groups. Enrichment analysis of WGCNA results indicated that the green module associated with G2 was enriched for amino acid metabolism, lipid metabolism and immunity-related pathway. Furthermore, the G3 associated turquoise module was dominated by stress response, detoxification and energy metabolism pathways. Together, high stocking density causes the occurrence of oxidative stress, disturbance to immune system and alteration of metabolism profiles in P. monodon, whereas medium density (G2) is favorable to maintain physiological homeostasis. The results provide theoretical support to optimize aquaculture practice and contribute valuable information for subsequent studies.

MicroRNAs (miRNAs) play crucial roles in regulating various biological processes in crustaceans, including stress responses. Under acute low salinity stress conditions, miRNAs exhibit dynamic expression patterns that significantly influence the physiological and molecular responses of the shrimp. However, research on miRNAs in P. monodon is very limited, and their functions under low salinity stress remain unclear. In this study, by using high-throughput sequencing technology, we identified miRNAs and investigated their regulatory mechanism in P. monodon under low salinity stress. A total of 118 miRNAs were differentially expressed after low salinity exposure. These miRNAs were found to target genes involved in metabolism, pathogen infection, immune response and stress signaling pathways. By modulating the expression of these target genes, miRNAs were able to fine-tune the stress response of P. monodon, thereby enhancing its tolerance to low salinity. This study provides new insights into the regulatory roles of miRNAs in the stress response of aquatic organisms and suggests potential targets for genetic improvement to enhance stress tolerance in P. monodon aquaculture.

Black tiger shrimp (Penaeus monodon) is the largest species of penaeid, being commercially cultured globally, ranking as the second most farmed species in the shrimp industry. However, with the transformation of shrimp aquaculture from semi-intensive to high-density farming, the concentration of ammonia nitrogen in the aquatic environment has increased, severely affecting the growth and survival of shrimps. To increase production efficiency, breeding new strains of shrimp with the trait of tolerance to high ammonia nitrogen is desired in the black tiger shrimp aquaculture. Previous studies have shown that glutamate dehydrogenase (GDH) and aspartate aminotransferase 2 (AST2) play important roles in the metabolism of ammonia nitrogen in crustaceans. In the present study, we conducted synteny analysis of PmGDH and PmAST2 in different species. The interactions of PmGDH with ammonium (NH₄⁺) and PmAST2 with aspartate were analyzed by docking. To develop molecule markers associated with ammonia nitrogen tolerance, SNPs of PmGDH and PmAST2 were identified by direct sequencing, genotyped by the SNaPshot technique, and characterized through genotype-phenotype association analysis by PLINK software version 1.9 in the three geographical populations, two families with different ammonia tolerance, and 120 susceptible and resistant individuals of black tiger shrimp. The results indicate that the GDH and AST2 genes are evolutionarily conserved in vertebrates, except for the black tiger shrimp, which suggests divergence in selective pressure between invertebrates and vertebrates. Notably, PmGDH may interact with NH₄⁺ via the residue Asp178 within loop 1 in the GdhA domain through a hydrogen bonding interaction, and PmAST2 may interact with aspartate via helix 1, sheet 1, loop 1, and loop 2, through both hydrogen bonding interactions and a salt bridge interaction. A total of 12 SNPs were detected in the exons of PmGDH and PmAST2. Among these candidate SNPs, the distributions of PmGDH-1227 and PmAST2-132 showed both significant differences in the genotype and allele association analysis between susceptible and resistant groups. Haplotype association analysis showed that three haplotypes exhibited significantly different distributions between susceptible and resistant groups. In conclusion, PmGDH-1227 and PmAST2-132 were associated with ammonia nitrogen tolerance, and these SNP markers are expected to contribute to marker-assisted selection (MAS) breeding programs to obtain new strains of Penaeus monodon.

This study comprehensively evaluates the phenotypic traits, nutritional profiles, and genetic diversity of three cultured populations of Portunus pelagicus from Guangdong Province, China, namely from Shenzhen (PpSZ), Zhuhai (PpZH), and Chaozhou (PpCZ). We analyzed key nutritional components, including moisture, ash, crude fat, crude protein, total sugar, amino acids, and fatty acids. Notably, significant differences in total sugar content (p < 0.05) were observed among populations, whereas no substantial variation was detected in the other nutritional parameters. PpSZ exhibited significantly higher levels of specific amino acids, especially essential amino acids (p < 0.05). Fatty acid composition revealed a more favorable nutritional profile in PpZH. Analysis of physiological markers such as total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and catalase (CAT) activities demonstrated comparable levels across populations, with no significant differences. Genetic diversity assessment revealed SNP densities of 6.583, 6.16, and 6.08 SNPs/Kb for PpSZ, PpZH, and PpCZ, respectively. The low polymorphism (PIC < 0.25) indicates limited genetic variation within the species. This study provides valuable insights into the biochemical, nutritional, and genetic characteristics of these populations, offering critical implications for the optimization of aquaculture practices and the conservation of genetic resources for this economically significant species.