Low survival and growth are the major problems in intensive culture of the Chinese shrimp Fenneropenaeus chinensis. We used net-chasing training to simulate predator-like threat to improve the survival and growth of F. chinensis reared at high stocking densities (up to 240 individuals m(-2)). The shrimps were trained three times a day under four chased intensities, control, 25%-, 50%- and 100%-exhausted, reared at densities of 240 individuals m(-2) in each intensity. After 40 days, the biochemistry (lactate concentration, enzyme activities of anaerobic and aerobic metabolism), behavioural indicators (tail-flipping speeds; time spent on stationary, walking and swimming), survival and growth were determined. The net-chasing training increased tail-flipping speeds due to the increased activities of phosphofructokinase, pyruvate kinase and lactate dehydrogenase in abdominal muscles. The shrimps spent less time on swimming and more time on stationary after chasing training. The survival rates were 54.44% in the control group, but ranging from 88.89% to 90.56% in the 25%-, 50%-, and 100%-exhausted groups. Most of dead shrimps lost their pleopods, periodpods and (or) uropods. The 50%- and 100%-exhausted chasing reduced the total food consumption due to high levels of hemolymph lactate, resulting in low growth rates in these groups. The shrimps showed elevated growth rates with no reduced ingestion in the 25%-exhausted group. We conclude that net-chasing increased the tail-flipping ability and suppressed the cannibalistic behaviour, increasing the survival of F. chinensis reared at the high densities. The low-intensity (25%-exhausted) chasing increased the growth rates due to shrimp having more energy available allocating for somatic growth.
