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To understand the fish diversity in the upper reaches of the Yangtze River in Chongqing, environmental DNA (eDNA) technology was used to analyze the fish diversity during a one-year water body sampling period from April 2021 to January 2022. The results showed that a total of 82 fish species (including Oreochromis, which was not identified to species level). 7 orders and 19 families and 63 genera were detected in the Jiangbei Section of the upper Yangtze River in Chongqing including 5 species of national key protected animals, 8 species of endemic animals in the upper reaches of Yangtze River and 8 exotic species. The number of fish species showed a seasonal trend of autumn > winter > summer > spring, among which Cyprinus carpio, Hypophthalmichthys nobilis, Pelteobagrus fulvidraco, Hemiculter tchangi and Ctenopharyngodon idella were all detected in the four seasons and had high sequence abundance. The Chao1 and ACE indices differed significantly between seasons (P<0.05) and the alpha diversity index in winter was higher than the three other seasons. The PCoA results showed that the heterogeneity between spring and summer samples was low and the species composition was similar, while the fish species composition in autumn and winter were significantly different and the heterogeneity was high. RDA analysis showed that water level, water flow and water temperature were the main factors affecting the seasonal distribution of the fish community. They were negatively correlated with water temperature and water flow, positively correlated with water level in spring and summer, and negatively correlated with water temperature and flow and positively correlated with water level in winter. Spearman's correlation test showed that water temperature was significantly negatively correlated with Shannon diversity, Chao1 index and ACE index (P<0.01); conductivity was negatively correlated with Coverage index (P<0.05), and water temperature, water flow was negatively correlated with Simp- son diversity (P<0.05). Overall, this study shows that eDNA technology can rapidly analyze fish species composition and distribution, and has great potential and importance in the monitoring fish resources in the Yangtze River. [ABSTRACT FROM AUTHOR]

Nowadays, the cultivation mode of Hyriopsis cumingii urgently needs transformation and upgrading, and realizing sustainable aquaculture lacks the selection of suitable algae and the exploration of culture conditions. This experiment is to evaluate combined effects of ration levels (low ration, medium ration and high ration) and temperature (13.0 ± 0.2°C, 23.0 ± 0.2°C, and 33.0 ± 0.2°C) on immune responses of H. cumingii. Activities of immune enzymes (alkaline phosphatase, superoxide dismutase, catalase and lysozyme) and expression of immune‐related genes (interleukin‐17 and inhibitor of apoptosis protein) in mussels were analysed during 21 days exposure period. Results suggested that the diatom Navicula pelliculosa was suitable algae for H. cumingii, the optimal ration level and temperature of H. cumingii were the medium ration and 23℃. Semi‐starvation, excessive dietary, low‐ or high‐temperature stimulated immune activities, and when beyond the immune regulation range, most immune enzyme activities decreased. Acute stress also stimulated expression of HcIL‐17 and IAP, and long‐term stress of discomfort temperature and ration levels led to immune dysfunction and affected expression of these genes. The study has practical significance in realizing the sustainable aquaculture of H. cumingii and provides a broader perspective regarding the water ecosystem. [ABSTRACT FROM AUTHOR]

Standard single‐exposure of calcein (CAL) was conducted on juvenile silver carp, Hypophthalmichthys molitrix, to examine its effects on antioxidant enzyme levels and lipid peroxidation. Juveniles were exposed to different concentrations of CAL solutions (0, 100, 300, 500 and 700 mg/L) for different immersion periods (12, 24, 48, 72 and 96 hr). Increased glutamate‐oxaloacetate transaminase, glutamate‐pyruvate transaminase and alkaline phosphatases activities were assumed to be due to CAL‐induced hepatic damage, probably because of the high potential of CAL to accumulate in fish hepatopancreas. Higher CAL concentrations (>300 mg/L) and prolonged immersion periods (>48 hr) could lead to greater toxicity in juvenile silver carp and, to a certain degree, damage the gills and hepatopancreas. The antioxidant responses in the gills and hepatopancreas result in successful elimination of the excess CAL‐induced reactive oxygen species for CAL exposure ≤24 hr. Our results confirmed that the toxic effects of CAL on antioxidant enzyme levels and lipid peroxidation in juvenile silver carp depended on both CAL concentrations and duration of exposure. Moreover, concentration of CAL solutions and the immersion period should be, respectively, restricted to ≤300 mg/L and ≤24 hr, when CAL is used for immersion marking juvenile silver carp. [ABSTRACT FROM AUTHOR]

Marking fish with fluorochrome dyes has the potential to produce detectable marks in otoliths, scales, fin rays, fin spines, and other bony structures based on differential staining of chemical dyes, and it is a widely used technique for mass-marking fish that included both teleosts and elasmobranchs. This technique, which has relatively economic advantages and simple marking process, can be applied to fish of all ages, and these fluorescent marks can be retained for several months and even years. Up to now, >200 fish species have been successfully marked by this marking technique. Fluorescent labeling is a practical and available marking technique for large-scale marking hatchery-reared fish. The methodology of fluorescent labeling is reviewed, including fluorochrome labeling dyes, application method, detection, and evaluation strategies. Aspects of practical applications, limitations, and supervision of fluorescent labeling are also discussed. [ABSTRACT FROM AUTHOR]