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The combined effects of temperature (23 and 27 °C), light intensity (1100 and 2 lux or ≈ 21.5 and 0.04 μEinst m−2 s respectively) and photoperiod (10 h light/14 h dark and 14 h light/10 h dark) on ovarian maturation and spawning performance of ablated pond-reared Penaeus merguiensis were investigated in a 51-day experiment. The results showed that temperature was the most influential factor, followed by light intensity, whereas the effect of photoperiod was minor. As the maturation process progressed, the effects of temperature and light intensity became stronger while that of photoperiod became less significant. Temperature significantly affected all the reproductive parameters assessed. Prawns in the 27 °C treatments outperformed those in the 23 °C treatments (P

An experiment was conducted to investigate the effect of light intensity just prior to and during spawning of Penaeus (Fenneropenaeus) merguiensis de Man in the laboratory. Neither the presence of light nor light intensity (0, 10 and 1100 lux) had a significant effect on the spawning process or hatching rate in P. merguiensis. Difference in the percentage of spawners, percentage of incomplete spawning, fecundity and hatching rate were all insignificant (P > 0.05) among the three light treatments. However, spawning was delayed (up to 21 min on average) under 1100 lux with a high percentage of incomplete spawning, compared with the Control (0 lux). For the first time, spawning behaviour of P. merguiensis was observed and fully described. The spawning process can be divided into four phases: dormant, pre-spawning, spawning and post-spawning by distinct behaviour of prawn broodstock. The dormant phase was characterized by a quiescent and non-feeding period, whereas movement of prawn broodstock was active during the pre-spawning and post-spawning phases. Depending on the individual, spawning was completed within 3-5 min. Prawns often stayed still on the water surface during spawning with occasional manoeuvres to change the position. After a short rest at the termination of the spawning phase, prawn broodstock re-exhibited active movement as in the pre-spawning phase, but showing conspicuous care to the deposited eggs. The role of light in controlling ovarian development and spawning, and the behaviour of prawn broodstock in relation to maximizing fertilization rate are discussed.

Critical thermal minima (CTMin) were determined for subadults of Penaeus merguiensis acclimated at 15, 18, 21 and 24 °C for 3 weeks. The effect of cooling rate on CTMin was also investigated. The CTMin of prawns from these respective acclimation groups were 5.3, 6.0, 7.4, 9.0 and 4.7, 5.4, 6.0, 7.3 °C at the cooling rate of 1 °C h−1 and 3 °C h−1 respectively. Both acclimation temperature and cooling rate had a significant effect (P