七种捕食性鱼类对中华绒螯蟹幼蟹捕食风险的评估

分别以鲤、鳜、斑点叉尾、黄颡鱼、瓦氏黄颡鱼、大口鲇和乌鳢作为捕食者,以中华绒螯蟹幼蟹作为猎物,在室内水泥池(2.4 m3)进行捕食试验。以日捕获率和日摄食率为指标,评估这些鱼类对幼蟹的捕食作用和危害程度,为提高湖泊幼蟹放流效果、建立蟹—鱼复合的优质高效养殖模式提供科学依据。在幼蟹完全暴露的条件下,经过多次(至少9次)重复的试验(短期1d和长期7d),鳜对不同大小的硬壳和软壳(刚蜕壳的)幼蟹没有任何捕食作用;黄颡鱼对硬壳和软壳幼蟹也没有捕食作用,但还需做进一步观察;虽然鲤、瓦氏黄颡鱼对硬壳蟹的捕获率低,但对软壳的幼蟹有较大的危害性,对幼蟹的日摄食率分别为0.070%、0.012%;大口鲇、斑点叉尾、乌鳢对幼蟹具有较强的捕食能力,对幼蟹的日摄食率分别为0.122%、0.188%和0.284%。根据这些研究结果,可以建议:(1)在池塘和湖泊河蟹养殖中,完全可以将鳜作为套养或混养对象,以期提高养殖效益;(2)在河蟹放养的湖泊,需要抑制乌鳢和大口鲇种群,适当减少鲤和瓦氏黄颡鱼丰度,以期减少这些鱼类的捕食作用,提高幼蟹存活率;(3)在河蟹养殖池塘,不能放养乌鳢、大口鲇、斑点叉尾、瓦氏黄颡鱼和鲤。

ASSESSMENT OF PREDATION RISKS OF SEVEN PREDACIOUS FISH ON JUVENILE CHINESE MITTEN CRAB (ERIOCHEIR SINENSIS)

The lake and pond cultures of Chinese mitten crab(Eriocheir sinensis) are two main farming modes with high commercial benefits in the Changjiang River basin.Unfortunately,recapture rates of the released crabs are often considerably lower mainly due to the predation of predacious fish.In order to provide scientific bases for improving the survival of the crab stocked in lakes and establishing a crab-fish polyculture mode with high returns on investment,a series of predation experiments of indoor cement pools were conducted to assess predation risks on juvenile E.sinensis by Cyprinus carpio,Siniperca chuatsi,Ictalurus punctatu,Pelteobagrus fulvidraco,Pelteobagrus vachelli,Silurus meridionalis and Channa argus.The minimum mouth width of all predators was more than 17.9 mm and the experimental crabs were 9.5-12.7 mm in carapace width and 0.49-1.82 g in body weight.The predation risk of each predacious fish on the exposed juvenile crabs was measured in terms of daily capture rate and daily consumption rate.In the present study,S.chuatsi and P.fulvidraco were not found to forage on juvenile crabs,either hard-or soft-shelled,and thus showed no predation risks on the crab.C.carpio and P.vachell were also not observed to prey on hard-shelled crabs in the 1-day-predation experiment,but to capture soft-shelled crabs in the 7-day-predation experiment,with low daily consumption rates(0.07% and 0.012%,respectively),which revealed that the two species were harmful to the crab and displayed relatively low predation risks.In all experiments,C.argus,I.punctatu and S.meridionalis can prey on both hard-and soft-shelled juvenile crabs and their daily consumption rates were 0.284%,0.188% and 0.122%,respectively,which indicated that the three species possessed strong predation ability and show high predation risks on the crab.Based upon the results of this study,three suggestions were listed as follow:(1) S.chuatsi and the crab may be stocked together in ponds and lakes for improving fishery benefits;(2) It was necessary to limit the population size of C.argus and S.meridionalis to the minimum level and maintain low abundance of C.carpio and P.vachelli in the crab-culturing lakes in order to increase the survival rate of the stocked crab;(3) Any one of C.argus,S.meridionalis,I.punctatus,P.vachelli and C.carpio with some predation risks on the crab must be not cultured in the crab-culturing ponds.