Metabolomics has been used extensively to identify crucial molecules and biochemical effects induced by environmental factors. To understand the effects of acute low-salinity stress on Fenneropenaeus chinensis, intestinal histological examination and untargeted metabonomic analysis of F. chinensis were performed after exposure to a salinity of 15 ppt for 3, 7, and 14 d. The histological examination revealed that acute stress resulted in most epithelial cells rupturing, leading to the dispersion of nuclei in the intestinal lumen after 14 days. Metabolomics analysis identified numerous differentially expressed metabolites (DEMs) at different time points after exposure to low-salinity stress, in which some DEMs were steadily downregulated at the early stage of stress and then gradually upregulated. We further screened 14 overlapping DEMs, in which other DEMs decreased significantly during low-salinity stress, apart from L-palmitoylcarnitine and vitamin A, with enrichments in phenylalanine, tyrosine and tryptophan biosynthesis, fatty acid and retinol metabolism, and ABC transporters. ABC transporters exhibit significant abnormalities and play a vital role in low-salinity stress. This study provides valuable insights into the molecular mechanisms underlying the responses of F. chinensis to acute salinity stress.

Salinity is an important environmental stress factor in mariculture. Shrimp intestines harbor dense and diverse microbial communities that maintain host health and anti-pathogen capabilities under salinity stress. In this study, 16s amplicon and transcriptome sequencing were used to analyze the intestine of Fenneropenaeus chinensis under low-salinity stress (15 ppt). This study aimed to investigate the response mechanisms of the intestinal microbiota and gene expression to acute low-salinity stress. The intestinal tissues of F. chinensis were analyzed using 16S microbiota and transcriptome sequencing. The microbiota analysis demonstrated that the relative abundances of Photobacterium and Vibrio decreased significantly, whereas Shewanella, Pseudomonas, Lactobacillus, Ralstonia, Colwellia, Cohaesibacter, Fusibacter, and Lachnospiraceae_NK4A136_group became the predominant communities. Transcriptome sequencing identified numerous differentially expressed genes (DEGs). The DEGs were clustered into many Gene Ontology terms and further enriched in some immunity- or metabolism-related Kyoto Encyclopedia of Genes and Genomes pathways, including various types of N-glycan biosynthesis, amino acid sugar and nucleotide sugar metabolism, and lysosome and fatty acid metabolism. Correlation analysis between microbiota and DEGs showed that changes in Pseudomonas, Ralstonia, Colwellia, and Cohaesibacter were positively correlated with immune-related genes such as peritrophin-1-like and mucin-2-like, and negatively correlated with caspase-1-like genes. Low-salinity stress caused changes in intestinal microorganisms and their gene expression, with a close correlation between them.

To explore the function of the period gene (Ec-per) in Exopalaemon carinicauda, we cloned the gene of 4611 bp with a 5′UTR of 201 bp, a 3′UTR of 813 bp, and an ORF of 3597 bp encoding 1198 amino acids. The predicted protein includes two PAS and one PERIOD domain. qPCR analysis revealed that Ec-per was expressed across all tissues tested at different developmental stages and during both embryonic and larval stages. Moreover, Ec-per oscillated rhythmically under different conditions of light-to-dark (L:D) ratios, including continuous darkness (0 L:24 D), where changes in the photoperiod influenced amplitude and phase shifts. The knockdown of Ec-per mRNA significantly reduced the expression of the circadian-related genes timeless (tim) and cryptochrome 1 (cry1) (p < 0.05). This suggests that Ec-per is an endogenous clock gene that may participate in molecular feedback loops and synergistically regulate the circadian rhythms through interacting with tim and cry1. RNA interference of Ec-per also markedly downregulated ecdysone receptor mRNA (p < 0.05), suggesting a positive role in the ovarian development of E. carinicauda. In situ hybridization further demonstrated that Ec-per is involved in oocyte proliferation and the accumulation of exogenous nutrients. This study provides new insights for promoting ovarian development and artificial breeding in crustaceans through optimized light-cycle management.

We previously found that period (per) may exert a positive regulatory effect on ovarian development under the modulation of circadian rhythms. This study further explores the function of the core clock gene timeless. Thus, we cloned the tim gene (Ec-tim) from the ridgetail white prawn, Exopalaemon carinicauda. The full-length Ec-tim cDNA sequence is 6102 bp in length and encodes a protein of 1543 amino acids with a conserved TIM domain. Quantitative real-time PCR (qPCR) analysis revealed that Ec-tim displays prominent eyestalk-specific expression in both adult and sexually mature individuals. Under different light–dark (L:D) cycles, Ec-tim exhibited regular oscillations under various L:D ratios within a 24 h period, and even under constant darkness (0 L:24 D) (p < 0.05), suggesting that tim is an endogenous clock gene. After RNAi-mediated silencing of Ec-tim, the transcript levels of key circadian clock genes, including per and cryptochrome 1 (cry1), were significantly downregulated relative to the control group (p < 0.01). In contrast, the mRNA level of the ecdysone receptor gene (EcR) was markedly upregulated (p < 0.01). These findings suggest that tim may regulate the expression of per and cry1 to form a trimeric complex, synergistically modulating circadian rhythms to further affect ovarian development in shrimp. Collectively, this study provides valuable references for further research on circadian regulation and reproductive development in crustaceans.

To elucidate the effects of pathogenic infection on the muscle quality and tissue structure of the shrimp, we explored the changes in muscle tissue quality and structure of the ridgetail white prawn (Exopalaemon carinicauda) after infection with Vibrio parahaemolyticus, WSSV, and co-infection with V. parahaemolyticus and WSSV, all through intramuscular injection of pathogens. Our results reflected that muscle tissue of healthy shrimps was tightly arranged and had neat muscle fibres and uniform texture. While compared with the control group, the muscle hardness, adhesiveness, elasticity, and chewiness of the shrimp in both single and co-infected groups were significantly decreased (). In addition, microscopic observation indicated that in each infected group, the muscle fibre gaps in the muscle tissue of the shrimp increased, the muscle density decreased, and even some muscle fibres swelled and broke. The above results suggested that the infection of pathogens significantly affected the shrimp’s muscle quality and tissue structure, which may be related to the pathogenic mechanisms of these pathogens. In actual shrimp farming, we should improve the shrimp’s muscle quality through a series of measures, such as enhancing disease resistance.