| With the development of ecological aquaculture pattern, warm water fish(Siganus guttatas) as a new variety of ecological aquaculture has been greatly promoted, and has been farming low temperatures in the northern regions such as Qingdao, Weihai and other regions. The reproduction, development and nutrients have been studied, but the effect of temperature on S. guttatas has yet to be supplemented. In this experiment, the thermal tolerance, growth, feeding and metabolism of different temperature on juvenile S. guttatas were studied.1. This study was aimed at assessing the critical thermal temperature maxima(CTmax), critical thermal temperature minima(CTmin), and acclimation response ratio of juvenile S. guttatus(2.163±0.450g) after acclimating to five preset temperatures(19℃, 22℃, 25℃, 28℃ and 31℃) for two weeks. In recent years, critical temperature method was commonly used as an effective tool to study the impact of temperature on fish after some researchers improved, and in this experiment critical temperature method was used to obtain the critical temperature, and then analyze the thermal tolerance characteristics of juvenile S. guttatas. Thermal tolerance experiment was set at a temperature variation rate of 1 ℃/h. The results showed that the critical thermal maximum(CTmax) and critical thermal minimum(CTmin) were 37.26℃、37.72℃、39.49℃、39.75℃、39.90℃ and 13.11℃、13.14℃、14.22℃、14.29℃、17.28℃, the lethal thermal maximum(LTmax) and lethal thermal minimum(LTmin) were 37.76℃、38.18℃、39.88℃、40.79℃、40.93℃ and 11.69℃、11.75℃、11.85℃、12.41℃、15.39℃. The test parameters all increased with increasing acclimation temperature. The thermal tolerance amplitude at 19℃, 22℃, 25℃, 28℃ and 31℃ was 24.15℃、24.58℃、25.27℃、25.46℃、22.62℃, respectively. The maximum(0.663) of the acclimation response ratio(ARR) at high temperatures is in the range of 22~25℃, while in low temperatures, the maximum(0.997) is in 31~28℃.The thermal tolerance polygon area of the juveniles within the range of acclimation temperature 19~31℃ was calculated as 296.085℃2. The results of acclimation response rate showed that juvenile S. guttatus have a high temperature tolerance value at higher acclimation temperature; otherwise there will be a relatively low temperature tolerance value. It was indicated that the thermal tolerance of S. guttatus was dependent on acclimation temperature.2. The rabbit fish(S. guttatus)(0.83±0.03)g were reared under different temperature to study the response of survival, growth, feeding rate(FR), food conversion efficiency(FCR) and digestive enzyme activities to temperature. The results showed that, the survival rate(SR) was more than 95% in all treatment during the experiment. The mortality rate at 19℃was higher than that in other treatment(P<0.05). The final weight, the final length, the weight gain rate(SGR) and the specific growth rate(SGR) of fish significantly increased(P<0.05) with increasing temperature in the range of 19~31℃: 31℃>27℃>24℃>19℃. The relationship between body weight at 31℃ and 27℃ and time was binomial, while it was linear at 23℃ and19℃. The food conversion efficiency was increased significantly with decreasing temperature in the range of 19~31 ℃(P<0.05). The relationship of food conversion efficiency and temperature was parabolic. It reached a minimum at 29.89℃. However, Feeding rate increased significantly with increasing temperature in the range of 19~31℃(P<0.05). The relationship of feeding rate and temperature was parabolic. It reached a maximum at 31.74℃. The activity of protease was significantly increasing with decreasing temperature(P<0.05). That at 19℃was highest and significantly higher than that at 27℃ and 31℃(P<0.05). There was no significantly difference among each group of the activity of lipase(P>0.05). The activity of amylase and maltase were the highest at 23℃, and significantly higher than that at 19℃ and 27℃(P<0.05). The results shows that 29.89~31.74℃ may be suitable temperature for the growth and feeding of juvenile rabbit fish. This information will be useful for developing culture techniques and extending culture area for the species.3. The effects of different acclimation temperature(19℃, 23℃, 27℃, 31℃) on the rabbit fish(S. guttatus) metabolic activity of juveniles. The results show that, GPT and GOT, LPL and HL activities were tended to increase with the temperature drop; CS and SDH activity was first increased and then decreased with temperature drop, 23℃ group activity was significantly higher than 19℃ and 31℃ group(P<0.05); 19℃ group GOT and GPT, PK and HK, LPL and HL activity was significantly higher than 27℃ and 31℃ group(P<0.05), LDH activity was significantly lower than the rest of the temperature group(P<0.05). There was no significant difference(P>0.05) between the rest of the temperature groups. These results showed that 19℃has been exceeded the suitable temperature range of juvenile fish. in order to resist the low temperature environment stress the basal metabolism of 19℃ group is higher than other temperature groups, fish use more fat and less anaerobic metabolic pathways for energy. |
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