The blotched snakehead Channa maculata is an important economical freshwater species in East Asia. However, there has been relatively little research conducted on the correlation between gender and gut microbes. In this study, 36 of 1000 blotched snakeheads were randomly selected for growth performance measurement and gut microbiota high-throughput sequencing. Results showed that microbial diversity, composition, and metabolic functions were altered by gender and growth performance except the microbial network. In our study, Proteobacteria were the most abundant phylum, with Fusobacteria showing enrichment in males and Bacteroidetes in females. Notably, phylum Deinococcus-Thermus was identified as a significant biomarker. The Cetobacterium was the most abundant genus-level taxon. Furthermore, gut microbes specializing in the production of gut-healthy substances, such as coenzymes and vitamins, were identified as biomarkers in the fast-growing group. Our investigation highlighted the impact of gender on the composition and abundance of gut microbial biomarkers in both males and females, thereby influencing differential growth performance through the modulation of specific metabolic functions.

Developing a low-protein feed is important for the sustainable advancement of aquaculture. The aim of this study was to investigate the effects of essential amino acid (EAA) supplementation in a low-protein diet on the growth, intestinal health, and microbiota of the juvenile blotched snakehead, Channa maculata in an 8-week trial conducted in a recirculating aquaculture system. Three isoenergetic diets were formulated to include a control group (48.66 % crude protein (CP), HP), a low protein group (42.54 % CP, LP), and a low protein supplementation EAA group (44.44 % CP, LP-AA). The results showed that significantly lower weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER), and feed efficiency ratio (FER) were observed in fish that were fed LP than in the HP and LP-AA groups (P < 0.05). The HP and LP-AA groups exhibited a significant increase in intestinal villus length, villus width, and muscular thickness compared to the LP group (P < 0.05). Additionally, the HP and LP-AA groups demonstrated significantly higher levels of intestinal total antioxidant capacity (T-AOC), catalase (CAT), and superoxide dismutase (SOD) and lower levels of malondialdehyde (MDA) compared to the LP group (P < 0.05). The apoptosis rate of intestinal cells in the LP group was significantly higher than those in the LP and HP groups (P < 0.05). The mRNA expression levels of superoxide dismutase (sod), nuclear factor kappa B p65 subunit (nfκb-p65), heat shock protein 70 (hsp70), and inhibitor of NF-κBα (iκba) in the intestine were significantly higher in the LP group than those in the HP and LP-AA groups (P < 0.05). The 16s RNA analysis indicated that EAA supplementation significantly increased the growth of Desulfovibrio and altered the intestinal microflora. The relative abundances of Firmicutes and Cyanobacteria were positively correlated with antioxidant parameters (CAT and T-AOC), whereas Desulfobacterota was negatively correlated with sod and T-AOC. The genera Bacillus, Bacteroides, and Rothia were associated with the favorable maintenance of gut health. In conclusion, dietary supplementation with EAAs to achieve a balanced amino acid profile could potentially reduce the dietary protein levels from 48.66 % to 44.44 % without adversely affecting the growth and intestinal health of juvenile blotched snakeheads.

A systematic study was conducted to identify reliable reference genes for normalization of gene expression analysis in the blotched snakehead Channa maculata under normal physiological conditions. Firstly, the partial complementary (c)DNA of nine candidate reference genes (actb, tmem104, ube2l3, ef1α, churc1, tmem256, rpl13a, sep15 and g6pd) were cloned from C. maculata. The expression levels of these genes were then assessed in embryos of different developmental stages and various tissue types of adult fish using quantitative real-time (qrt-)PCR. RefFinder algorithm was used to evaluate the expression stability of these genes based on their cycle-threshold (Ct ) values in the qrt-PCR analysis. Results showed that there was no single best reference gene for all stages of embryos and adult tissues tested. Furthermore, it was found that, among the nine candidate genes tested, actb and tmem104 were the most stable reference genes across adult tissue types, while sep15 and tmem256 were the most stable ones across developmental stages of embryos. These stable reference genes are recommended for normalization of gene expression analysis in C. maculata.