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Two environmental manipulation protocols were tested against a current maturation technique (CONTROL) in an 81-day experiment. PROTOCOL 1 mimicked changes in the natural environment from winter to spring when ovarian maturation and spawning in Penaeus merguiensis starts. PROTOCOL 2 evaluated whether a clear improvement of temperature from a fluctuation period to a stable one could help trigger ovarian maturation. In phase A (first 30 days) of the experiment, temperature and day length were gradually increased from 22 to 27 °C and from 10 to 14 h, respectively, while light intensity was stepwise reduced from 360 to 240, 120 and 5 lx for PROTOCOL 1. For PROTOCOL 2, light intensity and day length were manipulated as for PROTOCOL 1, but temperature was cycled from 22 to 27 °C every 3 days. In phase B (the following 30 days) temperature, light intensity and day length were stably maintained at optimal levels (27 °C, 5 lx and 14 h light, respectively). During phase B, the proportion of female prawns reaching stages III and IV was significantly (P

The effects of light intensity (I, 750 and 75 lx) and photoperiod (P, 12L/12D and 7L/5D) on moulting and growth of Penaeus merguiensis were investigated over 12 weeks under laboratory conditions. Both light intensity and photoperiod significantly (P 0.05), prawns cultured at 750 lx tended to moult more frequently. Sexual dimorphism was not observed within the range of tested prawns.

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

The effects of prawn age, size, and light intensity on spawning performance of pond-reared Penaeus merguiensis were studied by inducing spawning of prawn broodstock by eyestalk ablation under two different light intensities (bright, 1100 lx and dim, 2 lx) at three different known ages (7, 10, and 13 months old). For each age group (except the 13-month-old group), two distinguished size classes (large and small) were established to reveal the effect of prawn size. Results showed that light intensity did not affect spawning performance of prawns of different ages and sizes (P>0.05). In contrast, age had a significant effect on spawning performance of prawns (P

The effect of three levels of light intensity (BRIGHT: 1100 lux; DIM: 2 lux; and DARK: 0 lux) on ovarian maturation and spawning of Penaeus merguiensis was investigated. The proportion of spawners, latency period, spawning rate, fecundity, spawning interval and number of days spent at stage IV per spawn were not significantly different (P>0.05) among the three light intensity treatments. Compared to dim light, bright light did not adversely affect the maturation and reproductive performance of ablated prawns. However, the percentage of spawning at stage III (31.6%) and mortality (26.7%) were significantly higher in the DARK treatment (P

The effect of light intensity on ovarian maturation and spawning of unablated female Penaeus merguiensis was investigated in a 4 week experiment. The experiment had two different light intensity treatments: BRIGHT (1100 lx) and DIM (2 lx). At starting time, there were four groups of broodstock with four different ovarian maturation stages (II, III, IV and V) in each treatment. Results showed that light intensity plays an important role in controlling ovarian maturation of prawns, especially at the later stages (stages III and IV). Bright light showed an inhibitory effect, whereas dim light favoured ovarian maturation and spawning. Ovarian regression occurred in most stage III and stage IV prawns kept under bright light, while prawns at the same stages developed their ovaries further and spawned under dim light. Proportion of spawners (12.5%), mean number of spawns per prawn (0.12) and mean fecundity (87,300) of prawns were significantly lower (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.