网箱养殖大黄鱼两种间距分级栅分级效果的比较

A comparison of grading effects of grading panel with two different bar spacings for cage-cultured Pseudosciaena crocea

对770尾网箱养殖大黄鱼的生物学参数体宽（B）、体长（L）与体重（W）进行测定，运用幂函数拟合方法获得体重与其他两个参数的关系方程。为了达到按重量300g的分级要求，选择体宽为确定分级栅间距的依据，运用几何形态法、logistic曲线模型方法确定分级栅间距的理论值为34．66mm，用幂函数拟合方法得理论值为38．21mm。分级试验采用平均间距为33．01mm、37．95mm二种规格分级栅，对大黄鱼分级，结果表明：经过5～10min分级，间距33．01mm分级栅留存的大黄鱼中，达到分级标准的鱼（W≥300g）的最高比例为50．00％，平均为42．96％，留存下的鱼的平均体重296g；间距37．95mm的分级栅，留存的渔获中，体重高于300g的最大比例为73．33％，平均为43．76％，留存下的鱼的平均体重310g。使用平均间距37．95mm的分级栅，在周长为48m的深水网箱中进行分级操作后，留存的大黄鱼中，最小鱼体重为320g，分级效果良好。同时也表明用幂函数拟合方法计算分级栅间距比用几何形态法、Logistic曲线模型方法计算出的分级栅间距进行分级的效果要好。

Based on the measurements on 770 cage-cultured large yellow croakers,the relations between fish body width, length and their weight have been analyzed by means of regression equation. From the geometric morphological measurement on fish body, which are often used in estimating gillnet selectivity and from Logistic curve model, the theoretic bar spacing of the grading panel has been derived as 34.66 mm to meet the requirement of the grading standard 300 g. It was 38.21 mm derived from a power function regression. Grading effects were tested with two different grading spacings of 33.01 mm and 37.95 mm. For the 33.01 mm grading spacing grading panel, after 5 to 10 minutes of grading operation, the highest ratio of marketable fish which weigh more than 300 g was 50.00% of total retained by the grading panel. Their average body weight retained by the grading panel was 296 g. For the 37.95 mm grading spacing in the same conditions, the highest ratio, whose weight≥ 300 g was 73.33 % in the total retained by the grading panel. The average ratio was 41.65%. The average body weight of total fish retained by the grading panel was 310 g which was 25 g more than that of fish without sizing grade. Grading trials have been operated in a 48 m circle fish cage. All of the fish retained by the grading panel, when the bar spacing was set at 37.95 mm, were heavier than 300 g and the lowest body weight was 320 g. The results show that grading effect was better when the bar spacing was 37.95 mm, which was derived by means of a power function regression equation.