In order to investigate the effects of temperature on the growth performance, biochemical indexes and genes expression in juvenile hybrid sturgeon (Acipenser baerii♀ × Acipenser schrenckii♂), five temperature treatment groups (18 °C, 21 °C, 24 °C, 27 °C, 30 °C) were set in this study. After 25 days of domestication, the specific growth rate (SGR) and relative weight gain rate of juvenile sturgeon increased at first and then decreased with the increase in temperature in the range of 18–30 °C and reached the highest value at 21 °C. A quadratic equation was used to fit the regression equation of SGR and temperature (T). The result showed that the temperature of the maximum SGR is 23.45 °C. Moreover, the expression level of the growth hormone (gh) and the content of blood glucose (GLU) increased significantly at 21 °C, while the expression level of the growth hormone receptor (ghr) in the liver decreased significantly. When the temperature exceeded 27 °C, the thyroid hormone levels were significantly affected, and the levels of total antioxidants (T-AOC) and reduced glutathione (GSH) were significantly higher than those in the control group. In addition, with the increase in temperature, the expression levels of hsp70 and hsp90 in the liver increased significantly, while the expression level of the luteinizing hormone (lh) in the brain decreased significantly. To summarize, the effect of temperature on the growth and development of juvenile sturgeon mainly occurs through the effects of glucose metabolism, thyroid hormone level, total antioxidant capacity and growth-related genes. Therefore, in a temperature range between 21 and 24 °C, juvenile sturgeon can obtain the maximum growth rate and survival rate.

The purpose of this study was to investigate the periodic seasonal changes in endocrine activity and gonadal development of female rainbow trout (Oncorhynchus mykiss) in a high-altitude cold-water environment. The fish were sampled monthly from January to November and the levels of plasma hormones (estradiol (E₂), cortisol and thyroid hormones (TH_S)) and vitellogenin (VTG) were measured by ELISA. Moreover, the transcriptions of sex-related genes in the ovary, brain, and liver were detected by qRT-PCR. The results showed a seasonal fluctuation of plasma hormones and VTG together with the development of the ovary, which reached a peak from August to October. Similarly, the transcription of hypothalamic gonadotropin-releasing hormone-2 (cgnrh-2), hypothalamic gonadotropin-releasing hormone receptors (gnrhr) and follicle-stimulating hormone (fsh) in the brain varied from January to September, but the highest level was detected in September to November. In addition, the transcription of sex-related genes located in the ovary and liver increased significantly during August to October, accompanied by a continuous increase in the gonadosomatic index (GSI) and a decrease in the hepatosomatic index (HSI). Therefore, plasma hormones and sex-related genes regulate the development and maturation of O. mykiss oocytes with the change in seasons and peaked in November. The results of this study provide a reference for improving the efficiency of the artificial reproduction of O. mykiss.

Background: Rainbow trout (Oncorhynchus mykiss) is an important fishing resource in Yunnan. However, the oocyte quality and fecundity are particularly affected by environmental factors when fish are undergoing sexual maturation, which hinders the development of the O. mykiss industry.Results: Estradiol (E₂), thyroid hormones (THs), and sex-related genes transcription associated with gonadal development were analyzed in different growth stages of O. mykiss cultured in Yunnan. Females were classified into four growth stages: growth stage Ⅰ, growth stage Ⅱ, growth stage Ⅲ, and growth stage Ⅳ. Histological analysis found a correlated relationship between body growth and ovary development. Serum levels of E₂ and THs increased during ovarian development and reached the highest level at growth stage Ⅳ indicated that E₂ and THs play important roles in the development and maturation of oocytes in O. mykiss. Furthermore, real-time PCR analysis showed that the vitellogenin mRNA (vtg) transcription level increased significantly both in ovaries and liver during ovarian development, then reaching its peak at the post-vitellogenetic (growth stage Ⅳ) period. The same transcription trend was detected in the levels of ovarian estrogen receptors (ers). Conclusions: These results indicated that the high level of E₂ promotes the transcription of the vtg mediated by different types of ers, and then accelerates the maturation of oocytes, and THs also participate in the regulation of maturation of oocytes in cultured O. mykiss during the individual development in Yunnan.