Effect Of Environmental Factors On Growth Of Acipenser Schrenckii And Its Mechanism

This dissertation was based upon the concepts of fish ecophysiology, and investigated the regulations of the main important environmental factors in nature and aquaculture on growth and physiological system of Amur sturgeon, Acipenser schrenckii, which focused on the effects of hormones secreted by the neuroendocrine system in this process. The issues how Amur sturgeon adapted the various environments by changing its behaviors, physiological system, and growth strategies were discussed.This dissertation investigated the regulations of stocking density, photoperiod, water temperature, and water currents on growth and hormone secretion in neuroendocrine glands of Amur sturgeon. This research focused on how the brain neuroendocrine -growth hormone (GH) - insulin-like growth factor (IGF) axis and pituitary - thyroid axis controlled sturgeon growth during the acclimation to environmental factors. Serum total thyroxine (TT4), total triiodothyronine (TT3), free thyroxine (FT4), free triiodothyrinine (FT3), thyroid-stimulating hormone (TSH), GH, IGF-I, and cortisol levels were assayed contrasted to growth rates of sturgeon cultured in different environments. Meanwhile, RNA-DNA ratio in white muscle and liver tissues, body compositions, haemotological indices, serum biochemical indices, hepatosomatic index, and splenosomatic index were also investigated in this research.Ⅰ. Regulation of stocking density on growth by influencing the pituitary ?thyroidaxis and the brain neuroendocrine - GH - insulin-like growth factor (IGF) axisStocking density had negative effects on growth of sturgeon, specific growth rates (SGR) and growth efficiency (GE) decreased, and food conversion ratio (FCR) increased in higher density. But, the growth dispersion varied slimly during the experimental periods. Serum TT3, FT4, and FT3 levels were decreased significantly with increase of stocking density. While, serum GH, TSH and TT4 levels of different densities were not significantly different. The correlation coefficient between TSH and TT4 demonstrated the negative feedback effects of thyroid. Serum IGF-I level was also decreased with density increasing. Crude protein and fat contents in tissues were affected by stocking density. Furthermore, these parameters were correlated to density inversely. RNA-DNA ratio was in inverse proportion to density. Protein and fat contents significantly increased with body weight increasing. Serum cholesterol and lipids level were the lowest in the highest density experimental groups, whereas serum glutamic-oxaloacetic transaminase (GOT) was the highest.Ⅱ. Continuous light and dark photoperiods enhanced growth of Amur sturgeonThere was no significant difference in illumination perforce of juvenile Amur sturgeon when illumination was ranged from 1001x to 1 100 1x. However, juvenile show negative phototaxis when illumination was over 13 000 1x. Short-term (35 days) exposure to 24L:OD (PL), OD:24D (PD), and PLN (natural photoperiod, PN) could not affect growth of juveniles. But, growth was affected by long-term (8 months) exposure. PL and PD groups had the same growth rate, and grew faster than PN group. Serum TT3 and FT3 levels in PL and PD were much higher than those in PN, while these hormone levels in PL and PD were not significant different. But, serum GH, IGF-I, TSH, TT4, and FT4 levels in different photoperiods were not significant different. Crude protein content in liver of PN was significantly lower than that of PL and PD, the same to fat content in muscle. Inversely, crude fat content in liver of PN was significantly higher than that of PL and PD.Ⅲ. Growth controlled by hormones secreted by neuroendocine glands affected by water temperature during thermo-acclimationThe thermo-stress response occurred in Amur sturgeon at the beginning of thermo-acclimation to 26℃ . During this period, plasma cortisol and glucoseconcentrations elevated rapidly, then descent slowly. But, plasma cortisol level elevated again at 9d, and calmed down at 30d. Long-term thermo-accl...