鱼类早期资源调查中不同网具采集效率的研究

用网目为0.500和0.776mm的筛绢分别制成长度为1.5、2.0和2.5m的弶网、圆锥网和纺锤形网,采用网箱式、滤过式集苗桶和非滤过式集苗桶3种集苗器,于1998年5-6月在长江九江江段进行了采集仔鱼效果的比较研究。结果显示,弶网采集的数量最少,纺锤形网采集的数量最多。不同长度网具采集的数量没有显著差异,但长度为1.5m的圆锥网所采集仔鱼的规格明显小于长度为2.0和2.5m圆锥网所采集的。用网口面积分别为0.38m~2和0.20m~2的圆锥网组与不同类型集苗器进行比较,所采集仔鱼的数量和规格均没有差异。不同网目网具所采集仔鱼的数量没有显著差异,但网目为0.500mm圆锥网所采集仔鱼的平均规格显著小于网目为0.776mm圆锥网的。综合比较,以网目为0.500mm的纺锤形网的采样误差较小。

COLLECTING EFFICIENCY OF DIFFERENT NETS IN FIELD INVESTIGATION ON LARVAL FISH

A Chinese traditional drift sampler named "Qiang net", and two modifications of plankton nets were used for sampling larval fish in the Jiujiang reach of the Yangtze River from May 4 to June 30 in 1998 . The Qiang net was half-conical shaped and semi-submerged with a triangle open area above. One modification of plankton net was conical shaped and the other spindly shaped. The net shapes, the sizes of mesh (0. 500 and 0.776mm), the lengths of mesh cones (1.5, 2.0 and 2.5 meters), and the types of collection buckets (cage, filtrating bottle, and non- filtrating bottle), were regarded as factors affecting the collecting effects, in the studies.The sampling density (ind/m3) of the spindly net was the highest while that of the Qiang net was the lowest. However, the sampling size (total lenth of larvae) of Qiang net was larger than that of the others. No significance difference in sampling density was observed among the different net lengths and mesh sizes. Nevertheless, the sampling size of conical net made of 0. 500mm mesh was obviously shorter than that of 0.776mm mesh. Within the same size of mesh, the sampling size of the 1. 5m conical net was shorter than that of the 2.0 and 2.5m ones. There were no difference in sampling density and size among the three kinds of collection buckets.