As a small economic aquatic animal for human consumption, the crayfish Procambarus clarkii breeding was vigorously promoted in Anhui Province. In the present study, genetic analysis was conducted on 12 cultured populations in Anhui Province by microsatellite. The results showed that all twelve populations were showed a high genetic diversity (He=0.483-0.660, PIC=0.422-0.588). Among which the genetic diversity of Quanjiao population is highest, while lowest in Changfeng population. AMOVA analysis showed that most of the genetic variation was found within P. clarkii population (91.08%), while only 8.92% was found among populations. Genetic differentiation and genetic distance analysis showed that the overall differentiation level was moderate (Fst=0.078). Phylogenetic tree showed that all groups in Taihu and Susong County have a close relationship, Huoqiu and Quanjiao populations formed a sister relationship, and genetic distance between Xuanzhou and other populations was furthest, which mainly related to the parents origin. Additionally, populations experience the bottleneck effect, and inbreeding existed within or among populations, especially in Chngfeng and Xuanzhou populations. The result indicated the germplasm resources of cultured crayfish in Anhui have a tendency of decline, the parents should be updated periodically, and genetic exchanges among the populations should be strengthened.

Pseudobagrus vachellii (Richardson, 1846) is a commercially important freshwater fish species in China. To understand the effects of artificial breeding on the genetic diversity of three consecutive P. vachellii breeding populations (F1, F2, and F3) since 2012, a genetic analysis was conducted using polymorphic microsatellite markers. The mean allele number, expected heterozygosity, observed heterozygosity, and the polymorphic information content from generation F1 to F3 decreased from 7.75 to 5.63, from 0.77 to 0.63, from 0.83 to 0.77, and from 0.72 to 0.58, respectively. Analysis of molecular variance showed greater genetic divergence within the three generations (93.67%) than that among the generations (6.33%), and the overall differentiation level was moderate. Additionally, the lowest genetic differentiation was between F2 and F3 (F_st = 0.0484), and the highest was between F1 and F3 (F_st = 0.12864). Inbreeding occurred in each generation and was the highest in generation F3. Structural analysis showed that the three P. vachellii generations were most likely divided into two different genetic clusters. Although genetic diversity declined slightly in the mass selection lines after three breeding generations, overall genetic diversity was maintained at a relatively high level. To minimize the loss of genetic diversity and inbreeding in the subsequent breeding process, a moderate number of parents can be used for each generation. Information regarding the genetic diversity and structure of the selective P. vachellii breeding generations obtained in this study will be useful for future broodstock management and selective breeding programs.

Intensive culturing of hybrid yellow catfish (Pseudobagrus vachellii ♂ × Tachysurus fulvidraco ♀) has increased their mortality. Astragalus membranaceus has been used as an immune stimulant and antioxidant in fish for several years. A. membranaceus was decocted and mixed with the diet. After feeding for 28 d, the hybrid yellow catfish were challenged with Aeromonas hydrophila. To better understand the function of A. membranaceus in the defense of hybrid yellow catfish against A. hydrophila, we analyzed the spleen transcriptome data and relative percentage survival (RPS). There were 396 differentially expressed genes (DEGs) between the A. membranaceus and control groups at 24 h after A. hydrophila stimulation, including 263 upregulated and 133 downregulated DEGs. A significant enrichment of DEGs was found in the A. membranaceus group when the GO enrichment terms in the spleen were analyzed. The qRTPCRresults for the five upregulated and two downregulated DEGs from the spleen, intestine, and liver were consistent with the transcriptome data. The relative percentage survival of A. membranaceus was 85.71% after the fish were challenged with A. hydrophila.

Background: Onychostoma virgulatum is an endemic freshwater fish in South China, first described as a new species in 2009. However, little is known about this species and no complete mitochondrial genomes of O. virgulatum has been reported to date. This study seeks to elucidate the characteristics of the mitochondrial genome of O. virgulatum and investigate the phylogenetic relationships within the Acrossocheilinae subfamily, particularly among the genera Onychostoma, Acrossocheilus, and Folifer. Methods: The mitochondrial genome of O. virgulatum was sequenced and assembled. We analyzed its sequence length, nucleotide composition, and evolutionary relationships within the Acrossocheilinae by incorporate data from 58 previously published mitochondrial genomes. Results: The complete circular sequence is 16,606 bp in length and contains 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and a typical control region (D-loop), all arranged in a typical order. The genomic base composition is biased toward A+T content (56.5%), with 31.4% A, 25.1% T, 27.4% C, and 16.1% G. Among about 30 Acrossocheilina species, the nonsynonymous (Ka) to synonymous substitutions (Ks) for all 13 protein-coding genes (PCGs) are significantly less than 1, suggesting strong negative or purifying selection in these species. The phylogenetic trees inferred from the mitogenome and 13 PCGs of 58 Acrossocheilinae sequences consistently indicate that: (1) O. virgulatum shares the closest genetic relationship with Onychostoma barbatulum; (2) Acrossocheilinae species are clustered into three major clades, with neither Acrossocheilus nor Onychostoma forming monophyletic groups. Conclusions: This study provides new insights into the taxonomy and phylogenetic relationships of Acrossocheilinae, particularly O. virgulatum, contributing to a better understanding of the systematics, origin, and evolution of this subfamily.

Starvation is common in fish, particularly during the juvenile period, and is typically caused by environmental changes. However, the molecular mechanisms of juvenile Micropterus salmoides in response to starvation are still poorly understood. We elucidated changes in the serum physiology, transcriptome, and intestinal microbiome of M. salmoides after 14 days of starvation. Body weight and serum concentrations of glucose, cholesterol, triglycerides, and alkaline phosphatase significantly decreased during the starvation period. However, serum concentrations of aspartate transaminase and alanine transaminase were significantly elevated. Transcriptome analysis of liver tissues from commonly fed fish and starved fish revealed 1069 differentially expressed genes (DEGs), of which 211 were up‐regulated. In total, 586 DEGs were identified in the intestinal tissues, of which 166 were up‐regulated and 420 were down‐regulated. KEGG analysis revealed that starvation affected multiple pathways, particularly those related to energy, metabolism and immunity. Starvation limited fatty acid biosynthesis and elongation in the liver, down‐regulated immunity‐related genes in the intestine and promoted fatty acid degradation. The 16S rDNA analysis revealed that starvation altered intestinal microbiota homeostasis and increased intestinal Shannon diversity. Two opposite patterns of dominant genera emerged in commonly fed fish (most abundant genus is Mycoplasma) and in starved fish (most abundant genus is Cetobacterium). Starvation also increased the abundance of pathogens, including Plesiomonas and Aeromonas. Our study will provide the theoretical basis for assessing the starvation levels and nutritional status of juvenile fish and guidance for further studies on starvation in the context of fish physiology and health.