In this study, nine different treatments were tested on off-season reproductive performance of Penaeus semisulcatus for 60 days in a recirculating system, in round tanks (1.2-m diameter) situated in a greenhouse. A combination of raised temperature (28 degreesC) and shortened (10 h) or increased day length (14 h) was not sufficient to induce maturation in unablated females of P. semisulcatus. Unablated females showed no sign of ovarian development at a constant low temperature of 20 degreesC. Cyclic fluctuation (period of 10 days) of water temperature (20-28 degreesC) at local winter photoperiod regime (10-h illumination) induced successful maturation and even multiple spawnings within the same moulting period. Natural daylight supplementation (14-h illumination) did not produce any advantage over natural illumination (10 h). Unilateral eyestalk ablation had the most profound effect on the induction of ovarian development and spawning in this species. Even at a temperature of 20 degreesC, eyestalk-ablated females developed their ovaries up to the 4th stage but with still no spawning. It appears that P. semisulcatus requires not only optimal environmental conditions but also a certain stimulus such as ablation or temperature fluctuation for successful maturation and spawning in captivity during the winter season. Small tank size (1.2 m in diameter) did not inversely affect mating success of P semisulcatus at the sex ratio of 1:2 male/female and 10 shrimp/m(2) stocking density. The present results have demonstrated that eyestalk ablation or cyclic temperature fluctuation techniques can successfully be applied to obtain off-season spawning from P. semisulcatus broodstock in the subtropics. (C) 2003 Elsevier Science B.V. All rights reserved.