THE INFLUENCES TO TRANSPLANTATION OF ICEFISH (NEOSALANX TAIHUENSIS CHEN) ON EARLY-LIFE FEEDING AND GROWTH OF HEMICULTER LEUCISCULUS BASILEWSKY

Neosalanx taihuensis Chen is an important zooplanktivorous commercial fish, which was widely introduced into Chinese freshwaters. Transplantation of this species has induced decline and even extinction of native fish species in some waters. In this study, impacts of N. taihuensis transplantation on early growth and feeding of an indigenous zooplanktivorous fish Hemiculter leucisculus Basilewsky were investigated by comparing the juveniles of the latter in two reservoirs in the middle reach of the Yangtze River. Huangshi Reservoir (HSR) and Mengquan Reservoir (MQR) are geographically proximate and display similar nutrient regimes and native fish faunas. The major difference between the two water is that N. taihuensis has been transplanted in HSR but not in MQR. A total of 157 juvenile H. leucisculus was collected in late July and middle August in both reservoirs. The juveniles collected in late July aged from 14 to 23 days, and were similar in growth rate between the two waters. The juveniles collected in middle August aged from 20 to 49 days. Growth rate of juveniles in HSR was significantly smaller than those in MQR. Otolith growth trajectories showed that incremental width was not significantly different between the two reservoirs until the age of 25 days but narrower for juveniles in HSR than those in MQR after that. Diet analysis showed that food compositions of the juveniles younger than 25 days were similar between the two waters, composing mainly Rotifera, small-sized Cladocera and Cyclopoida. For juveniles older than 25 days, food compositions in HSR were similar to the younger juveniles, while the food compositions in MQR changed to large-sized Cladocera, insects, eggs and fish larvae. Spawning season of N. taihuensis is earlier than H. leucisculus in the middle reach of Yangtze River, and diet competition between the two species may occur after the later shifts from feeding on small-sized to large-sized zooplanktons. In HSR, N. taihuensis may induce the shortage of large-sized zooplanktons. As there was no enough large-sized zooplankton available to the juvenile H. leucisculus older than 25 days, they could only keep feeding on small-sized, which resulted in stunted growth of H. leucisculus juveniles older than 25 days compared to those in MQR.