Tor sinensis is an emerging aquaculture species in China, yet the effect of dietary protein on its hepatic and intestinal health remains unexplored. This study evaluated the effects of five diets designed to be isoenergetic and isolipidic with graded protein levels (28% to 40%) on juvenile T. sinensis (initial weight: 10 ± 0.4 g) over 60 days. Growth performance improved with increasing protein up to 34%, beyond which it plateaued. Regression analysis indicates that the optimal dietary protein level for both weight gain and specific growth rate is 34.3%. Hepatic antioxidant enzyme activities (SOD and CAT) were highest in the 34% protein group, while triglyceride content was lowest. Histological examination revealed minimal hepatocyte swelling, nuclear displacement, and lipid droplet accumulation at this protein level. Intestinal trypsin activity and villus morphology (height, width, and muscular thickness) were also optimized at 34% protein, though lipase and amylase activities remained unaffected. These findings demonstrate that a 34% dietary protein level supports optimal growth, enhances liver antioxidant capacity, and improves intestinal structure and function in juvenile T. sinensis, providing critical insights for its formulated feed development.

Nemacheilus subfusca is an endemic fish species in the lower Yarlung Zangbo River. Its habitats are potentially threatened by geological disturbances and anthropogenic activities, but information on population status remains limited. However, existing research has been largely confined to basic biology, with limited information on its population genetic structure and connectivity. Consequently, targeted investigations are urgently needed to provide a scientific basis for the conservation of this species. In this study, genetic diversity and population structure were analyzed in 50 individuals from two geographic populations (Motuo (MT) and Chayu (CY)) in the lower Yarlung Zangbo River, using mitochondrial cytb and D-loop markers. The populations exhibited high haplotype diversity but relatively low nucleotide diversity (cytb: H_d = 0.870, P_i = 0.00281; D-loop: H_d = 0.931, P_i = 0.01655). Notably, the MT population exhibited lower diversity levels compared to the CY population (cytb: H_d = 0.757, P_i = 0.00205; D-loop: H_d = 0.633, P_i = 0.00153). Substantial genetic differentiation was observed between the two populations (cytb: F_ST = 0.322; D-loop: F_ST = 0.733); The observed mitochondrial divergence did not provide clear evidence of species-level differentiation (cytb = 0.00331; D-loop = 0.02492). The ML phylogenetic tree and haplotype network revealed geographically associated clustering of the two populations, indicating geographic structuring of mitochondrial haplotypes. Furthermore, demographic analyses were consistent with a possible historical population expansion. In conclusion, The mitochondrial data revealed high haplotype diversity but relatively low nucleotide diversity, together with substantial genetic differentiation between the two sampled populations, forming geographically associated clusters. This study elucidates the genetic background of this species’ germplasm resources, providing baseline genetic information for future conservation and management of this species.

To determine the optimal water temperature range for artificial breeding and early development of Osteochilus salsburyi, six water temperature gradients (14, 18, 22, 26, 30, and 34 °C) were set to systematically investigate the effects of water temperature on artificial reproduction efficiency, embryonic development, the morphology of newly hatched larvae, larval growth performance, and the timing of organ development in O. salsburyi. The results showed that the spawning induction rate of O. salsburyi reached 100% at 14–30 °C. The fertilization rate and hatching rate peaked at 18–22 °C, and no fertilization was completed at 34 °C. The malformation rates of embryos and larvae showed a U-shaped change, with the lowest malformation rate at 18 °C, and the teratogenic effect of high-temperature stress was more significant. The embryonic development rate was significantly negatively correlated with water temperature, and the development duration was significantly shortened with increasing water temperature. Embryonic development was arrested and all embryos died at 34 °C, while hatching could be completed at 14 °C but with an excessively long cycle. The morphological indicators of newly hatched larvae showed differentiated sensitivity to water temperature; total length, pre-anal length, and body height were highly sensitive indicators, and larvae exhibited balanced and robust morphological development at 18–22 °C. The larval survival rate first increased and then decreased with increasing water temperature, reaching the highest rate at 22–26 °C. The absolute growth increment, relative growth increment, and specific growth rate (SGR) continued to increase with increasing water temperature. The timing of larval organ differentiation and behavioral development was significantly advanced with increasing water temperature. Late organ development of larvae was blocked at 14 °C, only early development was completed at 34°C, and the internal and external organs of larvae developed completely and in an orderly manner at 18–30 °C. In summary, the optimal water temperature for artificial breeding and early development of O. salsburyi is 18–26 °C, among which 18–22 °C is the best for artificial reproduction and 22–26 °C is optimal for larval rearing. The results can provide a scientific basis for the precise regulation of water temperature in large-scale seedling production of O. salsburyi.