Frequent bacterial outbreaks in aquaculture threaten commercial fish, with Plesiomonas shigelloides being notably common due to its lipa gene, a critical virulence factor. This study overexpressed the lipa gene in fish-derived P. shigelloides to investigate its impact on biofilm formation, LIPA activity, and bacterial adhesion. We infected Silurus meridionalis for 7 d to assess pathogenicity, observing symptoms, and collected the head kidney for transcriptome and proteomic analysis. Results were confirmed by qPCR and ELISA, and we performed GO classification, KEGG pathway, and protein interaction network analysis on differentially expressed immune proteins. The findings revealed that lipa overexpression increased biofilm formation (p < 0.01), lipoyl synthase activity (p < 0.01), and bacterial adhesion compared to wild-type strains, offering novel insights into its function. In Silurus meridionalis, this overexpression led to increased hemorrhaging in the anal and caudal fins compared to the wild-type and control groups. Furthermore, q-PCR and ELISA results demonstrated that the expression levels of NACHT/LRR/PYD domain-containing protein 4 (NLRP4), complement component 6 (C6), and lysozyme C (LZMC) correlated with the transcriptome and proteomic data. Overall, lipa overexpression enhances P. shigelloides virulence and intensifies the immune responses in Silurus meridionalis, providing insights into its pathogenic mechanism and supporting healthy breeding of Silurus meridionalis.
Standard length-weight relationships (LWRs) were estimated for five native fish species from the Chinese section of the Yalu River Basin, including Tanakia lanceolata (Temminck & Schlegel, 1846), Squalidus gracilis (Temminck & Schlegel, 1846), Pseudogobio longirostris Mori, 1934, Zacco platypus (Temminck & Schlegel, 1846), and Acheilognathus yamatsutae Mori, 1928. Fish specimens were collected in August 2022 by using traps in a variety of aquatic environments. In total, 514 individuals were measured for standard length (L) and weight (W), and LWRs were described by the equation W = aLb. The b values of LWRs ranged from 2.76164 to 3.17873, and all relationships showed high coefficients of determination (R2 = 0.9365-0.98907). According to the 95% confidence intervals of b, T. lanceolata, S. gracilis, and P. longirostris showed isometric growth; Z. platypus showed positive allometric growth; and A. yamatsutae showed negative allometric growth. These results provide the first LWR records of all five species in the Yalu River Basin, as well as a valuable reference for future research in this basin.
Trout were captured using gill nets at 206 mountain lakes to assess whether lake access difficulty or other abiotic lake characteristics influenced fish size. Lakes were 1,338-3,165 m in elevation and 0.2-22.9 ha in surface area; to reach them, off-road travel was 0-25.4 km in distance and 0-2,627 m in cumulative elevation gain, and the percent of off-road travel that was on a trail ranged from 0% to 100%. Cutthroat trout (Oncorhynchus clarkii) were similar in size (X = 273 mm) to rainbow trout (O. mykiss) ( X = 260 mm) and rainbow & times; cutthroat hybrids (X = 259 mm) but larger than brook trout (Salvelinus fontinalis) ( X = 218 mm). Trout were larger in lakes with an underlying shield lithology rather than acid volcanic, shale, and sedimentary rock lithologies, perhaps reflecting differences in rock weathering and therefore dissolved nutrients and minerals leaching into lakes. Trout were also larger in larger, higher elevation, southern-facing lakes with a more uniform shoreline. Larger lakes may provide more heterogeneous habitat, less overlap in habitat use between life stages (minimizing cannibalism), and more diverse, abundant, and stable food supplies. Geographical relief and aspect influence solar radiation, which in turn affects snowmelt, water temperature, and phytoplankton growth. The smallest effect size was for how much off-road travel was on a trail, perhaps because angling effort is so diffuse in high mountain lakes, and because contemporary anglers harvest few of the fish they catch in such settings, rendering angler access difficulty relatively unimportant to fish size structure.
Melanin-concentrating hormone (MCH) is known to be involved in the regulation of feeding and energy balance in mammals. However, the role of MCH in feeding by fish remains largely unknown. In this study, two transcript variants of pro-melanin-concentrating hormone (pmch) named pmcha and pmchb were cloned from Siberian sturgeon (Acipenser baerii). PMCHa encoded a protein of 179 amino acids, and PMCHb encoded a protein of 158 amino acid, both of which showed low identity (nearly 18%-27%) when compared with those of mammals, birds and teleost fish species. Both PMCHa and PMCHb contained a conserved MCH-related mature peptide located in the C-terminal region. Quantitative real-time polymerase chain reaction analysis showed that although pmcha was highly expressed in the hypothalamus, both pmcha and pmchb were highly expressed in the liver and cerebellum. Feeding promoted the mRNA expression of pmcha and pmchb in the hypothalamus at +1 h after feeding, and fasting for 1 d inhibited hypothalamic expression of pmcha and pmchb, suggesting that pmcha and pmchb might act as anorexigenic genes in feeding control. In addition, feeding inhibited the expression of pmcha and pmchb at +1 h after feeding but increased their expression levels at +3 h, and fasting for 10 d inhibited the mRNA expression of pmcha and pmchb in the liver, suggesting that pmcha and pmchb might play important roles in regulating energy metabolism in the liver. Taken together, pmcha and pmchb might participate in inhibiting food intake and energy metabolism in juvenile Siberian sturgeon. These findings provide molecular insights into the feeding regulation of Siberian sturgeon and may inform the development of optimized feeding strategies in sturgeon aquaculture.
