EFFECTS OF RELEASE SIZE ON SURVIVAL, GROWTH AND YIELD OF HATCHERY-REARED MANDARIN FISH STOCKED IN A SHALLOW YANGTZE LAKE

A tag-release-recapture study was conducted to evaluate effects of size at release on survival, growth and yield of hatchery-reared mandarin fish Siniperca chautsi fingerlings stocked in a shallow Yangtze lake. In May and June 2012, a total of 2400 juvenile mandarin fish were graded into three size groups, identified with coded wire tags and tail fin clipping, and released into Xiaosai Lake. Mandarin fish were collected after the lake drained in December 2012. Overall, a total of 973 mandarin fish individuals were captured, with an average survival rate of 40.5%. Survival rate of large sized group (63%) is more than three times higher than that of small sized group (19.5%) and 1.5 times higher than that of middle sized group (39.1%). The mean final length and weight of mandarin fish increased with the increase of release size and showed significant difference among groups. Yield was significantly affected by release size, which was the highest in large sized group and the lowest in small sized group. The net income of stocked mandarin fish increased with the increase of fish size at release. Our results indicated that mandarin fish size at release can have a major impact on success of hatchery releases, and it is suggested that the optimum release size of mandarin fish should not be less than 50 mm in Xiaosai Lake.