分级对银鲫生长和个体大小差异的影响

在室内水槽进行12周的饲养实验以检验分级对银鲫生长和鱼群内个体大小差异的影响。用隔网将实验水槽分为两部分，每个水槽内放养10尾大鱼（体重8.0~9.0 g）和10尾小鱼（体重6.5~7.5 g），分级时将个体大小相近的10尾鱼分布在隔网同一侧。实验中，3组鱼分别隔1周、2周或4周分级1次，1组鱼不进行分级作为对照。鱼摄食率和生长率随分级间隔时间缩短而降低。实验结束时，隔1周分级1次的鱼体重低于对照组，隔4周分级1次的鱼体重与对照组无显著差异。实验结束时被分级的鱼群中大鱼体重的变异系数高于小鱼，表明大鱼对分级操作更敏感。本实验结果表明,分级未能明显提高银鲫生长速度和降低鱼群内个体大小的差异程度。

Effect of size grading on growth and size variation ofgibel carp (Carassius auratus gibelio)

The effect of size grading on growth and size variation in group-housed gibel carp(Carassius auratus gibelio) was examined in a 12-week experiment.Four treatments were established: three groups of fish were graded at intervals of 1,2,or 4 weeks,respectively,while one group without gradation served as a control.The fish were reared in 20 tanks,each was divided into two parts by a medial net.Ten large fish(body weight 8.0-9.0 g) and 10 small fish(body weight 6.5-7.5 g) were distributed in each of the tanks.For size grading,the fish of similar body size in each tank were hand selected,and redistributed in same part of the tank.The results of the experiment indicated specific growth rate(SGR) declined with the increase of the grading frequency.At the end of the experiment,body weight of the fish graded once every week was lower than that of the control,while there was no significant difference in SGR between the control and fish graded once every 4 weeks.In the graded fish,coefficient of variance in final weight was higher in the large fish than the small fish,suggesting the large fish may be more sensitive to the grading operation than the small fish.Our results reveal size grading fails to improve growth performance and size variation in group-housed gibel carp.