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Abstract The morphological variation in Schizothorax oconnori, Schizothorax waltoni, and their natural hybrids was examined using conventional and image‐based analysis approaches. In total, 38 specimens of S. oconnori, 35 of S. waltoni, and 37 natural hybrids were collected from the Shigatse to the Lhasa section of the Yarlung Zangbo River during June and July 2021. A total of 21 morphometric, 4 meristic, and 27 truss variables were employed for the classification of S. oconnori, S. waltoni, and natural hybrids. Principal component analysis (PCA) and factor analysis (FA), as well as discriminant function analysis (DFA) and cluster analysis (CA), were conducted to identify differences based on traditional and truss measurements. Four principal components explained 75.92% of the variation among the morphometric characters, while five principal components accounted for 79.69% of the variation among the truss distances. FA results showed that factor 1 was associated with head shape, and factor 2 was associated with fins based on morphometric characters. Among the truss characters, factor 1 was related to head shape, and factor 2 was related to chest shape. In DFA, morphometric measurements achieved higher accuracy (100%) compared to truss distances (94.55%). The head morphology of hybrids exhibited intermediate traits between S. oconnori and S. waltoni. Both morphometry‐based and truss‐based clustering indicated that the morphology of natural hybrids leaned toward S. oconnori. In conclusion, the combination of morphometric and truss analysis is beneficial for classifying S. oconnori, S. waltoni, and their natural hybrids. The presence of natural hybrids could be considered an evolutionary response to the differentiation of nutritional and spatial niches in the middle Yarlung Zangbo River.

Elizabethkingia miricola (E. miricola) is a significant pathogen that causes the crooked head disease in black spotted frogs. This disease has plagued numerous frog farms in China and has resulted in substantial losses to the frog farming industry. Nonetheless, the exact mechanism that causes the disease in frogs remains unknown. In this study, transcriptomic and microbiomic analyses were conducted to analyze frog samples infected with E. miricola to reveal the infection mechanism of the pathogen. Liver transcriptomic analysis indicated that the livers of infected frogs had 1469 differentially expressed genes when compared with an uninfected group. These DEGs are mainly involved in immunity and metabolism, including neutrophil extracellular trap formation, the NOD-like receptor signaling pathway, leukocyte transendothelial migration, chemokine signaling pathway, Fc gamma R-mediated phagocytosis, and “metabolism”-related pathways such as the pentose phosphate pathway, carbon metabolism, glycerophospholipid metabolism, and glycerolipid metabolism. Similarly, 4737 DEGs were found in the kidney of infected frogs. These DEGs are mainly involved in immunity, including neutrophil extracellular trap formation, the NOD-like receptor signaling pathway, B cell receptor signaling pathway, C-type lectin receptor signaling pathway, complement and coagulation cascade, and Toll-like receptor signaling pathway. Ten immune-associated DEGs were screened in liver and kidney DEGs, respectively. And it was hypothesized that E. miricola infection could influence the host immune response. Microbiome analysis results showed that some opportunistic pathogens such as Citrobacter, Shigella, and Providencia were significantly elevated (p < 0.05) in infected frogs. Additionally, functional prediction confirmed that most of the microbiota in infected frogs were linked to metabolism-related KEGG pathways. In this study, the screened genes linked to immunity showed an association with the gut microbiome. The majority of these genes were found to be linked with the abundance of opportunistic pathogens. The results showed that E. miricola infection led to the downregulation of immune and metabolic-related genes, which led to the inhibition of immune function and metabolic disorder, and then increased the abundance of opportunistic pathogens in the gut microbiota. The findings of this study offer a preliminary foundation for comprehending the pathogenic processes of E. miricola infection in black spotted frogs.

In order to explore the spatial layout of fish assemblages and their related environmental factors, a survey of species composition was conducted in the Anning River. From 2018 to 2021, 28 sites at 987–2,077 m in altitude were surveyed, gathering 64 species in total, of which 60 were native and 4 were exotic. Fifteen of the species sampled were indigenous to the upper Yangtze River, and two were classified as critically endangered or endangered. Fish communities displayed significant upstream-to-downstream variation. There are two site-groups, one covering upstream and tributaries and the other covering midstream and downstream. The upstream-tributary fish assemblages had a dominance of Nemacheilidae and Schizothoracinae, which are plateau species with habitat preferences for boulders and fast-flowing water. Conversely, the mid-downstream fish assemblages had a dominance of Gobioninae, Cyprininae, Bagridae and Siluridae, which are common river species that prefer slow-flowing water. The spatial patterns of these fish communities were chiefly affected by altitude and substratum composition. The fish assemblage pattern was consistent with the zonation concept because the fish communities changed abruptly and clearly along the upstream–downstream axis. The findings of this study offer a crucial research foundation for comprehending the fish assemblages of mountainous rivers, which will be conducive to biodiversity management and habitat preservation of aquatic species.

In the present study, we investigated the age, growth, and reproductive characteristics of Euchiloglanis davidi, a species of Sisoridae fishes, from the Yalong River, China. Fish samples were collected from the tributaries of the middle and lower Yalong River in May 2013 and December 2015. Their standard length ranged from 67 to 190 mm, and the total weight ranged from 3.42 to 75.06 g. The age and growth pattern of E. davidi were determined using the vertebra. Furthermore, the sampled fish were categorized into 10 age groups (1–10 years old): the maximum age was 10 years and 9 years for male and female fish, respectively. The relationship between the standard length and weight was expressed as W = 6.744 × 10−5 L2.653, and the t-test showed allometric growth. The growth of E. davidi was defined by the von Bertalanffy growth function, described as Lt = 260.8(1−e−0.104(t+1.942)), Wt = 173.5(1−e−0.104(t+1.942))2.653, respectively. The growth inflection point was observed at 7.44 years, with corresponding length and weight values of 162.50 mm and 49.46 g. The fecundity ranged from 105 to 352 eggs, with an average of 205 eggs. The relative fecundity of weight (FW) ranged from 2.90 to 8.98 eggs/g, and the relative fecundity of length (FL) ranged from 0.71 to 2.11 eggs/mm. Altogether, these characteristics of slow growth and low fecundity demonstrated the vulnerability of E. davidi to exploitation in the middle and lower reaches of the Yalong River.

Due to a sharp decline in resources, Schizothorax waltoni Regan and Percocypris retrodorslis have been listed as wildlife under second-class protection in China. Under culture conditions, the early development and allometric growth patterns of S. waltoni and P. retrodorslis were researched from the hatching stage to 60 DPHs (days post-hatching), and a sampling of ten to fifteen larvae was made every day, followed by measurements with Axio Vision 4.8 software (Carl Zeiss AG, Jena, Germany). Morphological indicators included the anal fin length, the body depth, the body depth at the anus level, the caudal fin length, the dorsal fin length, the eye diameter, the head length, the head depth, the pectoral fin length, the tail length, the trunk length, the snout length, the total length, and the ventral fin length. Based on the morphology development of S. waltoni Regan and P. retrodorslis, four periods of larval growth were identified: pre-flexion larvae at 0–14 DPHs and 0–16 DPHs; flexion larvae at 14–23 DPHs and 16–26 DPHs, post-flexion larvae at 23–50 DPHs and 26–52 DPHs, and the juvenile stage. In newly hatched larvae, most organs and body parts were not differentiated, and they successively developed within 26 DPHs. The depletion of the yolk sac was observed at 23 DPHs and 25 DPHs. Allometric growth mainly occurs in the head and tail regions, indicating that body parts related to feeding and swimming behaviors were more important than the other parts. In addition, the growth pattern shows that the development of organs gives priority to the functions of gill respiration, sensation, exogenous feeding, and swimming. The inflection points of body part growth patterns only appeared before 40 DAH, so future studies should concentrate focus on developing the best feeding from the first feeding to 40 DAH. These outcomes were discussed with regard to the ontogeny of the functional morphology in relation to ecology and aquaculture. It is expected that this research can provide valuable perspectives in species conservation.

This study was conducted to evaluate the effect of dietary protein levels on growth performance, muscle composition, digestive enzymes activities, hemolymph biochemical indices and ovary development of pre-adult red swamp crayfish Procambarus clarkii (initial weight = 12.86 ± 0.10 g). Six isoenergetic diets (fish meal, soybean meal, gluten, and shrimp powder as main protein sources) were formulated to contain graded levels of 20.70 %, 24.70 %, 30.56 %, 35.77 %, 41.12 % and 44.64 % crude protein. Each diet was assigned to triplicate groups of 15 experimental crayfish (10 female and 5 male) for 8 weeks. Our results showed that weight gain (WG) increased with dietary protein supplementation from 20.7% to 35.77%, and then decreased with further increases in dietary protein. Broken-line regression analysis based on WG showed that the optimal dietary protein level for maximum growth performance of crayfish was 39.60 %. Feed conversion ratio (FCR) exhibited an opposite trend as observed in WG, with the lowest in crayfish fed the 30.56 % or 35.77 % protein diet. Protein efficiency ratio (PER) in crayfish fed the 41.12 % or 44.64 % protein diet was significantly lower than that in crayfish fed the 20.70–30.56 % protein diet. Hepatosomatic index (HSI) value of crayfish decreased with dietary protein supplementation and achieved minimum values at 35.77 % or 41.12 % protein diet. The highest crude protein content of tail muscle was found in crayfish fed the diet containing 35.77 % or 41.12 % protein. Activities of protease and lipase in both hepatopancreas and intestine were significantly affected by dietary protein levels, while amylase activity showed no significant difference. Dietary protein also significantly induced the contents of hemolymph total protein, albumin, globulin, glucose, total cholesterol and low-density lipoprotein, along with aspartate transaminase and alanine transaminase activities. Moreover, histological analysis revealed that the ovary development of most female crayfish fed the 35.77–41.12 % protein diet were at stage V, which had a higher frequency of mature oocytes than that of females fed other protein diets. Thus, these results provide the theoretical basis for feed formulation to determine the appropriate protein requirement of pre-adult red swamp crayfish.