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.