Effect of light intensity on maturation and spawning of ablated female Penaeus merguiensis

Abstract

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<0.05). A trend of increasing fecundity with an increase in light intensity was observed. Also, the hypothesis of whether the prawn eye is the only light receptor involved in ovarian maturation and spawning was tested by covering the remaining eye of ablated prawns with prepared caps made from black heat-shrinkable tubing (polyolefin). These prawns were held under 1100 lux (BRI-COV treatment) and 2 lux (DIM-COV) with the DARK treatment as the control group. The proportion of spawners was lowest in the BRI-COV treatment and highest in the DARK treatment (P<0.05), whereas there was no significant difference between these two treatments and the DIM-COV treatment. The DARK treatment, however, had a significantly higher spawning rate (P<0.05). The significantly higher percentage of spawning at stage III and less time spent at stage IV per spawn of prawns in the DARK treatment (P<0.05) compared with the DIM-COV and BRI-COV treatments suggest that the prawn eye may not be the only light receptor involving in ovarian maturation and spawning in P. merguiensis.