摘要:
目前一般较大的湖泊水库放养鱼类的回捕率颇低,逃鱼是重要原因之一。为了确定拦鱼用的网和栅所应采取的规格,测量了2,227尾(3—16厘米)鲢、鳙、草、青鱼种的全长,最大周长、头宽、颅宽的各个数值,推算出全长与最大周长、头宽、颅宽的迥归方程式及它们的95%的可信限。通过实验,观察到在流水条件下,鱼种能溯水穿越较自身最大周长为小的拦网网目或较头宽为小的拦栅栅距而逃逸。作者称这种能力为“穿拦系数”(用Kg 或Kp 表示)。并测出在武昌东湖某些生活污水进水口处,1973年3—4月份白鲢鱼种的穿拦系数按Kg 计算为1.5,按Kp 计算为1.2。作者建议在静水或出水口处,设置拦鱼用的拦网的网目长度不得超过所投放色种的最大周长的95%的可信限的下限的1/2,各种拦栅的栅距不得超过鱼种的头宽的95%可信限的下限。而在流水条件下,在确定所应采取的拦网网目或拦栅栅距时,还应该考虑“穿拦系数”在内。文末附有检索表,列举了鲢、鳙、草、青鱼种(3—16厘米)相应于全长值的最大周长值、头宽值、颅宽值以及它们的95%可信限的上限和下限的各个数值,供确定拦网网目和拦栅栅距的规格时参考。
Abstract:
The rather low recapture rate of the implanted fish in many sizable lakes andreservoirs at present is due,for one thing,to the fleeing of the implanted fingerlings.In order to establish a set of standards on the nettings and fences to be installedfor sake of preventing the fingerlings from escaping,the total length (L) and themaximal girth (MG) of the body,as well as the width of head (WH) and the widthof the paired parietal bones of cranium (WP) of 2227 fingerlings of four“domestic”fish (Hypophthalmichthys,Aristichthys,Ctenopharyngodon and Mylopharyngodon),ranging from 3 to 16 cm in total length,have been measured,and therefrom theregressions of MG,WH and WP on L,together with their 95% confidence intervals,have been worked out.It is demonstrated,experimently,that under lotic conditions,fingerlings againstthe current are capable of“squeezing”through meshes of which the circumference issmaller than the MG,or through interstices of which the width is smaller than the WH.Such capability can be measured in terms of what the authors call as“penetrant coef-ficient”,designated by either Kg or Kp.For Hypophthalmichthys fingerlings,Kg was determined as 1.5,and Kp as 1.2,based upon the data obtained from some sewage-containing inlets of Lake Tung-Huduring March and April,1973.The authors propose that under ordinary still-water conditions,nettings to beinstalled for preventing escaping should have their mesh-length not longer than 1/2the lower limit of the 95% confidence interval for the MG of the fingerlings to bestocked,and fences of all sorts should have their interstices not wider than the lowerlimit of the 95% confidence interval for the WH of the fingerlings to be implanted.Under running-water conditions,moreover,allowance should be made for the penetrantcoefficient.As an appendix,numerical values of the MG,WH,WP,corresponding to the Lof the fingerlings for each of the four species are tabulated,and values of the upperand lower limits of their 95% confidence intervals are also given for reference.
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