Temperature is an important factor in the physiological processes of aquatic organisms and can seriously affect several chemical and biological processes in their bodies, including respiratory metabolism, antioxidant capacity, immune capacity, and signal transduction. In this study, physiological, transcriptomic, and metabolomic analyses were used to investigate the response of Penaeus vannamei to cold stress. The results indicated that cold stress disrupted nucleotide metabolism and inhibited gluconeogenesis. However, shrimp exhibited response mechanisms in order to enhance cold tolerance, regulating changes in key genes and metabolites in amino acid and lipid metabolism to increase energy supply and protect cell membrane stability. In addition, the response included regulating Ca²⁺ pumps and ion channels to maintain intracellular ion homeostasis and osmotic balance. When the temperature dropped further, oxidative damage occurred due to overwhelming of the antioxidant defense system, and immune function was inhibited. This research provides some references regarding the molecular mechanisms involved in responding to cold stress and potential strategies to improve cold tolerance in P. vannamei; these are important references for studying the cold stress response of shrimp.

The presence of intermuscular bones severely affects the edibility and value-added processing of crucian carp (Carassius auratus), becoming a constraint to the high-quality development of its industry. Our previous study identified bmp6 as the key osteogenic regulator and successfully developed a new crucian carp strain lacking intermuscular bones (WUCI) using CRISPR/Cas9 technology. To accelerate its industrialization, we comprehensively assessed WUCI’s growth performance, hematological parameters, antioxidant capacity, innate immunity, and disease resistance. The results demonstrated that the WUCI exhibited significant growth performance compared to the wild-type crucian carp (WT), with significantly higher weight gain (WG) and specific growth rate (SGR) (p < 0.05) from one month to four months of age. The α-amylase (α-AL) activity of the liver and intestines of WUCI was significantly higher than that of WT. WUCI also displayed enhanced intestinal antioxidant capacity, with superoxide dismutase (SOD) and catalase (CAT) activities significantly higher than those in WT (p < 0.05). The malondialdehyde (MDA) content in the spleen of WUCI was significantly lower than that of WT (p < 0.05); no differences were observed in the liver and intestines (p > 0.05). Additionally, hepatic acid phosphatase (ACP) activity in WUCI was significantly higher than that in WT (p < 0.05). In contrast, splenic ACP and intestinal alkaline phosphatase (ALP) activities were significantly lower than those in WT (p < 0.05). Notably, the iron concentration in the serum was significantly higher in WUCI than in the WT (p < 0.05). Meanwhile, WUCI exhibited significantly lower a expression of hepcidin, TF, and TFR1 mRNA in the liver compared to WT (p < 0.05), while FPN mRNA expression was significantly higher (p < 0.05). Routine blood tests revealed significantly lower WBC in WUCI compared to that of WT (p < 0.05). Following an Aeromonas hydrophila challenge, WT demonstrated a rapid transcriptional induction of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) and immunoregulatory mediators (IL-10, TGF-β), with mRNA levels reaching maximal expression at 24 h post-infection (hpi) followed by progressive attenuation. In contrast, WUCI exhibited a delayed immune activation profile characterized by the peak expression of TNF-α, IL-1β, IL-6, and IL-10 transcripts after 72 hpi, with the maximum transcript abundance remaining lower than corresponding peak values observed in WT at 24 hpi. Finally, we observed that the mortality rate of WUCI was slightly higher post A. hydrophila infection when compared to WT, but was not significant (p > 0.05). In conclusion, this study provides a comprehensive evaluation of WUCI, revealing its distinct growth advantages, physiological adaptations, and immune function, presenting its potential for aquaculture breeding applications.

Aeromonas salmonicida, the causative agent of furunculosis, poses a serious threat to salmonid aquaculture, but its pathogenicity in rare cold-water fish species remains insufficiently characterized. This study reports the first isolation and characterization of a pathogenic A. salmonicida strain (Ag001) from diseased Thymallus arcticus grubei in China. Multilocus sequence typing (MLST), together with 16S rRNA, gyrB, and vapA gene analyses and phylogenetic characterization, identified the isolate as A. salmonicida subsp. salmonicida ST2. In intraperitoneal challenge assays using six bacterial dose groups and PBS controls, Ag001 showed high virulence toward T. arcticus grubei [LD50: 3.08 × 10³ CFU/mL (95% CI: 9.42 × 10²–1.01 × 10⁴ CFU/mL), equivalent to 7.16 × 10¹ CFU/g (95% CI: 2.19 × 10¹–2.34 × 10² CFU/g)] and Oncorhynchus mykiss [LD50: 3.16 × 10⁴ CFU/mL (95% CI: 1.19 × 10⁴–8.38 × 10⁴ CFU/mL), equivalent to 3.46 × 10¹ CFU/g (95% CI: 1.31 × 10¹–9.17 × 10¹ CFU/g)]. Comparative histopathological examination of spleen, liver, and kidney tissues from diseased and healthy fish revealed splenic necrosis, hepatic degeneration, and renal tubular damage in diseased fish. Genomic analysis identified complete T2SS and T3SS secretion systems, along with eight virulence-associated genes including aerA, hlyA, and vapA, suggesting that secretion systems and virulence factors may contribute to pathogenicity. Antimicrobial susceptibility testing showed susceptibility to enrofloxacin, neomycin, and doxycycline, but resistance to several other tested agents. These findings provide information on the host range, pathogenicity, genomic virulence features, and potential treatment options for A. salmonicida ST2 in cold-water aquaculture systems.