Influences of light intensity and photoperiod on moulting and growth of Penaeus merguiensis cultured under laboratory conditions.

Abstract

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) influenced the percentage weight gain (PWG), but did not influence moult frequency or moult interval. Mean PWG of prawns cultured at 750 lx was 198.4%, significantly (P<0.01) higher than those cultured at 75 lx (168.1%). Imposing two light/dark cycles (7L/5D) in 24 h resulted in a significantly higher growth of prawns (P<0.05) than the normal photoperiod (12L/12D). Prawns cultured at 750 lx had a lower food conversion ratio (FCR, 1.485) than those cultured at 75 lx (1.590, P<0.05). The effect of light intensity on prawn growth was found to be stronger and more immediate than that of photoperiod. There was no interaction between light intensity and photoperiod. Although not significantly different (P>0.05), prawns cultured at 750 lx tended to moult more frequently. Sexual dimorphism was not observed within the range of tested prawns.