| The present study was conducted in Liujiaxia Reservoir and the experimentalanimals used in the study were stocked into3m×3m×3m net cages. Firstly, the fish(115.72±8.9g) tested were divided into three groups and each group had three parallelgroups. They were designated as stocking density1(SD1), stocking density2(SD2)and stocking density3(SD3) respectively. The experiment was carried out from May2011to March2012. Results as follows;1. Assessing the effects of stocking densities on growth, body composition andlevels of plasma cortisol of rainbow troutThe objective of this section was to evaluate the effects of stocking densities in netcage on growth, fish biomass, body composition and plasma cortisol levels ofOncorhynchus mykiss. At the end of the experiment the body weights were751.5±40.8g,657.2±39.2g,587.8±31.8g respectively and the differences weresignificant among the three groups (P<0.05). The fish biomass showed that higherstocking densities resulted in lower values. Specific growth rate (SGR) and feedconversion ratio decreased with the increase in stocking density during these twoperiods (i.e. From July to November and from January to March of the following year)(P<0.05). In lower density treatments (SD1), the SGRs were signicantly higher thanthose of the other groups. Similarly, from July to November higher stocking densityresulted in lower FCR. In body composition, there was no significant effect fromdifferen stocking density on both ash and moisture in the experiment. Fish in SD1hadlower content of crude fat than those in SD2and SD3during above two periods(P<0.05). However, content of crude protein of SD1were higher when comparedwith SD2and SD3(P<0.05) in these times. Moreover, in January and March of thefollowing year, fish stocked in higher density released a higher levels of plasma cortisol (P<0.05).2. Effects of different stocking density on the levels of thyrioid hormone andplasma lipids in Oncorhynchus mykissThe objective of this section was to evaluate the effects of stocking density on freetriiodothyronine (FT3), free thyroxine (FT4), triglyceride (TG) and total cholesterin(TC) levels in the blood, IGF-I expression in the liver and intestine, and TR-αexpression in the liver and kidney of Oncorhynchus mykiss reared in net cages. Theresults showed that FT3and FT4levels decreased gradually as the stocking densityincreased, and they were positively associated with culture time before November. TGlevel decreased as the stocking density increased while TC level increased as thestocking density increased and they were negatively associated with culturetemperature. Moreover, TG level in the SD3was significantly lower than that in theSD1in November, and there were significant differences among the three treatmentsin January of the following year (P <0.05). Additionally, the expression levels ofIGF-I and TR-α also decreased gradually as the stocking density increased. Theseresults indicate that high stocking density could become a stressor for O. mykiss andthat would reduce FT3and FT4levels in the blood, thereby affect the growth anddevelopment of fish. Furthermore, the change trend of special growth rate (SGR)confirmed this conclusion. The reduced level of thyroid hormone resulted in lowerexpression of TR-α. There was a correlation between thyroid hormone and theexpression of IGF-I, and whether the thyroid hormone regulates the expression ofIGF-I await further study.3. Molecular cloning of VDR-a and VDR mRNA expression as well as blood Ca2+levels under stocking density of net cage in rainbow troutWe cloned complete cDNA of VDR-a from kidney of Oncorhynchus mykiss.Results indicate that the length of the cDNA of VDR-a was2606bp encoding theprotein of797amino acids, which contained domains A/B, C, D and E/F. Real-timequantitative PCR analysis showed that higher stocking density resulted in lowerrelative expression of mRNA in kidney and liver. The expression of VDR-a decreased significantly (P<0.05) when the culturing time lasted and the stocking densityincreased. The content of Ca2+in blood was lower as the stocking density increased.The results above show that higher stocking density weakened the active transport ofCa2+. Lower content of Ca2+led to lower expression of VDR-a in kidney and liveraccordingly. The effects of culture time to the expression of VDR-a were realizedthrough the stocking density.4. Effects of stocking densities on haematological indices and immune genesexpression in rainbow troutThe objective of this section was to evaluate the effects of stocking density onhaematological indices and immune genes expression in rainbow trout. The resultsshowed that WBCs decreased gradually as the stocking density increased, meawhileRBCs and content of Hb also were positively associated with stocking density. InJanuary and March of the following year, RBCs and Hb of SD3were significantlyhigher than those of the other groups (P <0.05). In July, September and November,TP decreased as the stocking density increased while Urea level and activity of CKincreased as the stocking density increased (P<0.05). Through semi-quantitativeRT-PCR, we found the expression of MHC-Ι mRNA existed in the9tissues. However,there was little mRNA expression of IgM in heart, stomach, brain, and intestine.Quantitative real-time PCR showed that in July, the expression levels of MHC-Ι ofSD3were higher than those of the other groups in the four tissues (P<0.05).Additionly, in spleen and head kidney, the expression levels of IgM increasedgradually as the stocking density increased (P<0.05). Our results indicate thatdifferent stocking density can affect the rainbow trout and higher stocking density asan adverse factor resulted into negative effects on the fish.5. Molecular cloning of hepatic glucose-6-phosphatase from rainbow trout:response of its expression and levels of plasma glucose at different stockingdensityWe cloned complete cDNA of G6Pase from liver of Oncorhynchus mykiss. Results indicate that the length of the cDNA of G6Pase was1728bp encoding theprotein of364amino acids. Real-time quantitative PCR analysis showed that theexpression of G6Pase in liver increased as the stocking density increased inNovember and March of the following year. Similarly, the expression of G6Pase inkidney increased as the stocking density increased too in March of the following year(P<0.05). However, levels of blood glucose were negatively associated with stockingdensity. In November and March of the following year, blood glucose levels of SD1were significantly higher than those of SD2and SD3(P<0.05). From the results wededuced more expression of G6Pase could promote the gluconeogenesis, howeverhigher stocking density made the fish need more energy so the levels of blood glucose... |
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