Optimum temperatures for growth and feeding of juvenile Amur sturgeon Acipenser schrenckii

The juvenile Amur sturgeon Acipenser schrenckii had good appetites and grew in allometry during the experiment period at water temperatures of 17℃,20℃,23℃ and 26℃.During the experimental period,water temperature,pH,DO and ammonia-N level were measured once a day respectively.The major environmental factors were controlled at the same levels in each experimental tank where DO was beyond (5.5mg/L.)This experiment lasted 35 days.The results show that the specific growth rate (SGR),daily weight gain (DWG),food conversion ratio (FCR) and feeding ration (FR) were influenced significantly by water temperature.During the first experimental stage (0-15 d),sturgeons cultured at 20℃ had the highest daily weight gain (DWG),while the smallest DWG occurred in those cultured at 26℃.However,during the later stage (16-35d),the sturgeons cultured at 23℃ grew the faster than those at other temperatures.After statistical analysis,it showed that sturgeons cultured at 23℃ grew fastest in all experimental treatments.During the experimental period,the fish were fed enough food,but food consumption of fish varied with different temperatures.Feeding ration increased continually with temperature,while maximum ration reached an optimum at intermediate temperature,then declined.Fish reared at 20℃ and 23℃ had good appetites constantly,while feeding ration of fish cultured at 26℃ was lower than others until fish acclimatized themselves to this water temperature.The results showed that the maximum feeding ration (2.74±0.04)% (BW/d) occurred in 23℃ treatment.The lowest FCR,(1.18±0.05)%,was found in 23℃ experimental treatments,which indicated that fish stocked at 23℃ had lowest feed coefficient or highest feed conversion efficiency.The correlations between these parameters and water temperature (T) could be described by nonlinear regression models:SGR=(-12.93)+(1.418)T+(-0.033)T~(2)(P0.01,r=0.9081),FR=(-5.324)+(0.719)T+(-0.016)T~(2)(P0.01,r=0.9707),and FCR=(7.111)+(-0.564)T+(0.013)T~(2)(P0.01,r=0.9030).The optimum temperature for SGR and FCR were 21.53℃ and 21.03℃ respectively calculated by above equations.The optimum temperature for growth was lower than that for food consumption which was 22.33℃.In comparison with the prior studies,it implies the optimum temperature for fish growth is generally lower than the optimum temperature for food consumption,because of the increasing costs of maintenance at higher temperatures.In addition,the results suggest that lower and higher water temperatures should be adverse to growth of Amur sturgeon beyond the optimum temperature range.