Length composition, age, sex ratio and maturity of landed nigorobuna Carassius buergeri grandoculis in Lake Biwa

摘要

To protect and enhance the nigorobuna Carassius buergeri grandoculis fishery, a minimum total length limit of 220 mm (170 mm standard length) was established in Lake Biwa in April 2007. The length composition, age, sex ratio and gonadosomatic index (GSI) of nigorobuna landed by gill-net during February and March from 2006 to 2008 were investigated to evaluate the regulation. The percentage of catches smaller than 170 mm in standard length decreased from 18.9% in 2006 to 2.8% in 2008. The catches were dominated by fish of age 1 and age 2, and females accounted for about 70% of the catches. Females with low GSI values were classified as male with low commercial value, and they accounted for about 30% of the catches in 2008. Delaying the fishing season would reduce the unreasonable catch.