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The yellow catfish (Pelteobagrus fulvidraco) is an economically important species in China and East Asia. However, with the development of high-density farming, bacterial diseases of yellow catfish are becoming increasingly serious. In mammals, autophagy participates in an intracellular innate defense pathway in response to bacterial and viral infections. Among these signaling pathways, stimulator of interferon genes (STING) combines with a ring diode produced by the cyclic GMP-AMP synthase (cGAS) and activates the immune response and autophagy of pathogenic microorganisms. The cGAS-STING signaling pathway in fishes remains largely unexplored. This study found that cGAS and STING exhibited both conserved gene structure and gene synteny in various species of teleosts and diverse species of vertebrates. Expression profiling revealed that the transcription levels of cGAS and STING in immune tissues were significantly up-regulated within 48 h after stimulation with Aeromonas hydrophila or Edwardsiella tarda. Our results demonstrated that the expression levels of TBK1 and IRF3 in the cGAS-STING pathway were significantly up-regulated in the liver, kidney, and spleen, suggesting that this pathway was triggered and activated within 48 h by stimulation with exogenous A. hydrophila. Analyses conducted through Transmission Electron Microscopy (TEM) and marker genes showed that autophagic hyperactivation occurred in the liver, spleen, and kidney of hybrid yellow catfish after infection with A. hydrophila or E. tarda. Taken together, the results indicate that cGAS and STING function are critical mediators of antibacterial immunity in the yellow catfish, and that the cGAS-STING signaling pathway is involved in mediating antibacterial defenses.

Due to factors such as overfishing, hydropower development, and water pollution, their wild populations have drastically declined, with many species being classified as endangered or vulnerable. Understanding the driving factors behind the gut microbiota of cold-water fish holds significant implications for conservation. Therefore, to investigate the influence of different factors on the gut microbes of cold-water fish, 112 gut samples from farmed and wild habitats were collected from Schizothorax wangchiachii (herbivorous), Schizothorax kozlovi (omnivorous) and Percocypris pingi (carnivorous), in the Jinping Dahewan range of lower reaches of the Yalong River. The results of 16 S rRNA gene sequencing of the gut contents showed that habitat was the major factor influencing the gut microbes of the three cold-water fishes. In terms of microbial composition, farmed cold-water fish exhibited a dominant bacterial phylum, Proteobacteria (82 %), while those in wild environment presented multiple dominant taxa, such as Proteobacteria (38 %), Fusobacteria (30 %), Firmicutes (11 %), and Cyanobacteria (11 %). Gut microbial diversity, both α diversity and β diversity, in wild cold-water fish was significantly higher than that in farmed individuals. Network complexity of gut microbiota was notably higher in wild cold-water fish than in farmed individuals. From farmed to wild environments, the relative influence of deterministic processes in the gut microbiota assembly mechanism of cold-water fish gradually diminishes, while the contribution of stochastic processes steadily increases. The gut microbiota construction mechanism in farmed cold-water fish was primarily influenced by deterministic processes of homogeneous selection, while in wild cold-water fish, it was mainly driven by stochastic processes of homogeneous dispersal. Overall, this study is an important reference for the study of the gut microbiota of cold-water fish and the conservation of their wild populations.

One novel catfish (Chinese called it ‘Gou nian’) widely cultured in China shares the same name with Ictalurus punctatus introduced from America, but is morphologically closed to genus Silurus. For years, the novel catfish was speculated to be an artificial hybrid of S. asotus and S. meridionalis. Therefore, we investigated the correct taxonomic status and origin of the novel catfish by means of morphological and molecular approaches. First, the novel ‘Gou nian’ could not be distinguished from S. asotus and S. meridionalis through anatomical observation, however, it was morphologically similar to S. asotus. Then, the novel ‘Gou nian’ was found not a hybrid of S. asotus and S. meridionalis based on the identification of ITS-2 and RAG-2, moreover, the analysis of COI barcoding found it more likely to be S. asotus. The phylogenic and population genetic analysis of Cyt b showed that the novel ‘Gou nian’ belonged to a taxonomic branch of S. asotus from the Liao River. The results convincingly indicated that the novel catfish is S. asotus and may originate from Northern China. The findings also provided useful implications for aquaculture management of the species.