Global warming is one of the most common environmental challenges faced by cold-water fish farming. Intestinal barrier function, gut microbiota, and gut microbial metabolites are significantly altered under heat stress, posing serious obstacles to the healthy artificial culture of rainbow trout. However, the molecular mechanisms underlying intestinal injury in rainbow trout under heat stress remain unclear. In the present study, the optimal growth temperature for rainbow trout (16 °C) was used for the control group, and the maximum temperature tolerated by rainbow trout (24 °C) was used for the heat stress group, which was subjected to heat stress for 21 days. The mechanism of intestinal injury in rainbow trout under heat stress was explored by combining animal histology, 16S rRNA gene amplicon sequencing, ultra-high performance liquid chromatography-mass spectrometry, and transcriptome sequencing. The results showed that the antioxidant capacity of rainbow trout was enhanced under heat stress, the levels of stress-related hormones were significantly increased, and the relative expression of genes related to heat stress proteins was significantly increased, indicating that the heat stress model of rainbow trout was successfully established. Secondly, the intestinal tract of rainbow trout showed inflammatory pathological characteristics under heat stress, with increased permeability, activation of the inflammatory factor signaling pathway, and increased relative expression of inflammatory factor genes, suggesting that the intestinal barrier function was impaired. Thirdly, heat stress caused an imbalance of intestinal commensal microbiota and changes in intestinal metabolites in rainbow trout, which participated in the stress response mainly by affecting lipid metabolism and amino acid metabolism. Finally, heat stress promoted intestinal injury in rainbow trout by activating the peroxisome proliferator-activated receptor-α signaling pathway. These results not only expand the understanding of fish stress physiology and regulation mechanisms, but also provide a scientific basis for healthy artificial culture and the reduction of rainbow trout production costs.

As the global climate warms, more creatures are threatened by high temperatures, especially cold-water fish such as rainbow trout. Evidence has demonstrated that long noncoding RNAs (lncRNAs) play a pivotal role in regulating heat stress in animals, but we have little understanding of this regulatory mechanism. The present study aimed to identify potential key lncRNAs involved in regulating acute heat stress in rainbow trout. lncRNA and mRNA expression profiles of rainbow trout head kidney were analyzed via high-throughput RNA sequencing, which exhibited that 1256 lncRNAs (802 up-regulation, 454 down-regulation) and 604 mRNAs (353 up-regulation, 251 down-regulation) were differentially expressed. These differentially expressed genes were confirmed to be primarily associated with immune regulation, apoptosis, and metabolic process signaling pathways through Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis and coding-noncoding co-expression network analysis. These results suggested that 18 key lncRNA-mRNA pairs are essential in regulating acute heat stress in rainbow trout. Overall, these analyses showed the effects of heat stress on various physiological functions in rainbow trout at the transcriptome level, providing a theoretical basis for improving the production and breeding of rainbow trout and the selection of new heat-resistant varieties.

The effects of heat stress on aquatic animals are increasingly being discerned, but little is known about the effects of heat stress on muscle meat quality or the flavor of muscle. This study aimed to evaluate the effects of heat stress on the muscle antioxidant properties, structural and physical properties (e.g., pH, muscle color, shear force, and expressible moisture), chemical composition (e.g., nucleotides, organic acids, amino acids, and minerals), and volatile substances of rainbow trout. We observed that the antioxidant capacity of muscle decreased after stress experiments at 22.5 °C for 24 h. The content of inflammatory factors notably increased (p < 0.05), the pH value and red value of muscle decreased (p < 0.05), the interfiber space increased, and several muscle fibers were broken. Heat stress changed the contents of nucleotides, organic acids, minerals, and amino acids in muscle. The contents of IMP and AMP, which play an important role in the flavor of muscle, decreased (p < 0.05). The contents of two amino acids that provide a sweet taste decreased; those of five amino acids that provide a bitter taste increased (p < 0.05). Heat stress also affected the amount and type of volatile substances in muscle, which affected muscle odor. These results suggest that heat stress may exert adverse effects on the oxidative stability, structure, meat quality, and flavor of muscle, requiring attention and prevention.

Global warming represents one of the most pressing environmental challenges to cold-water fish farming. Heat stress markedly alters the mucosal symbiotic microbiota and intestinal microbial metabolites in fish, posing substantial barriers to the healthy artificial breeding of rainbow trout (Oncorhynchus mykiss). However, the relationship between mucosal commensal microbiota, intestinal metabolites, and host environmental adaptability under heat stress remains poorly understood. In this study, rainbow trout reared at optimal temperature (16 °C) served as controls, while those exposed to maximum tolerated temperature (24 °C, 21 d) comprised the heat stress group. Using 16S rRNA amplicon sequencing and ultra-high-performance liquid chromatography–mass spectrometry (UHPLC-MS), we analysed the mucosal commensal microbiota—including gastrointestinal digesta, gastrointestinal mucosa, skin mucus, and gill mucosa—and intestinal metabolites of rainbow trout under heat stress conditions to explore adaptive and regulatory mechanisms. Analysis of microbial composition and diversity revealed that heat stress exerted the greatest impact on the diversity of gill and skin mucus microbiota, followed by gastrointestinal digesta, with relatively minor effects on the gastrointestinal mucosa. At the phylum level, Proteobacteria, Firmicutes, and Bacteroidetes were predominant in the stomach, intestine, and surface mucosa. At the genus level, Acinetobacter showed the greatest increase in abundance in skin and gill mucosa under heat stress, while Enterobacteriaceae exhibited the most pronounced increase in intestinal digesta, gastric digesta, and gastric mucosa. Differential metabolites in the intestinal digesta under heat stress were predominantly enriched in pathways associated with amino acid metabolism, particularly tryptophan metabolism. This study provides a comprehensive characterisation of microbiota and metabolic profile alterations in rainbow trout under heat stress condition, offering a theoretical foundation for understanding the response mechanisms of fish commensal microbiota to thermal stress.

Ziwuling black goat (ZBG) is the main breed of indigenous goat for meat, wool, and skin in northwest china. However, the population has faced a sharp decline in the past few decades, mainly due to the declining efficiency of goat farming, which has led to the reluctance of farmers to raise goats. Litter size (LS), horn or no horn (HN), wool color (WC), and body conformation (BC) traits are the four main economic indicators of goat culture, which have the potential to increase population growth rate. The aim of the study was to identify potential genomic regions associated with body conformation traits of ZBG using genome-wide association studies (GWAS), and to identify molecular markers that influence LS, HN, WC, and BC traits of goats for the improvement of genetic resources of goats. In the study, we used the Illumina sequencing platform to re-sequence the genomes of 318 ZBG (12 males and 306 females) belonging to natural populations in 4 different regions, including LS, HN, WC, body height (BH), body weight (BW), body diagonal length (BL), and chest circumference (CC). The GWAS were conducted to identify candidate genes with different phenotypes which laid a foundation for further studies on the biological functions of these genes. A total of 41 single nucleotide polymorphisms (SNPs) and 89 candidate genes were obtained in 7 phenotypes of goats. Among them, 5 SNPs and 18 genes were significantly associated with the LS traits in goats, and these loci were located on 2 chromosomes. There are 5 SNPs and 10 genes significantly associated with the HN traits, and these loci are located on 5 chromosomes. There were 18 SNPs and 31 genes significantly associated with the WC traits, and these loci were located on 16 chromosomes. There are 6 SNPs and 13 genes significantly associated with the BH traits, and these loci are located on 6 chromosomes. There are 2 SNPs and 7 genes were significantly associated with the BL traits, and these loci were located on 2 chromosomes. There are 2 SNPs and 2 genes significantly associated with the BW traits, and these loci are located on 2 chromosomes. There are 3 SNPs and 8 genes were significantly associated with the CC traits, and these loci were located on 3 chromosomes. We investigated the molecular genetic mechanism of LS, HN, WC, and BC traits of ZBG by analyzing its genome data. The study identified a series of SNPs and candidate genes associated with growth and reproductive traits, which helped accelerate the breeding process of goat breeds.

Since viral hemorrhagic septicemia virus (VHSV) was first identified in rainbow trout, it has evolved into four major genotypes in the process of infecting multiple hosts. The different levels of virulence among genotypes of VHSV are caused by genetic evolution. In this study, the complete genome sequences of global VHSV strains were obtained from the GenBank database and their genetic relationships were analyzed. The maximum likelihood (ML) phylogenetic tree based on the complete genomes of VHSV showed that globally, VHSV strains evolved into two region-specific clades, namely the European clade and the North American clade. North American VSHV strains are more conserved than European strains. Both European and North American strains are subjected to purifying selection. All VHSV proteins are gathered into their region-specific clusters in genetic distance space. Furthermore, North American and Asian strains have organized glycosylation sites in their G protein. An early Japanese strain, KRRV9822, which clusters into the North American clade, has undergone potential recombination. Together, the region-specific genetic relationship and mutation characteristics of global VHSV strains were revealed with a crucial perspective for epidemiological research on VHSV.