Effects of photoperiod and light intensity on the rearing performance and phototactic behaviour of kuruma shrimp Marsupenaeus japonicus larvae and postlarvae

Abstract We examined the effects of photoperiod and light intensity on survival and growth of kuruma shrimp ( Marsupenaeus japonicus ) across developmental stages from the zoea–mysis (ZM) to the postlarval (PL) stage, as well as the effect of light intensity on phototactic behaviour. During the ZM stage, growth tended to be higher ( p = 0.052) under photoperiods including a dark phase (12L:12D and 18L:6D) than under continuous light (24L:0D) and tended to be higher ( p = 0.059) under low to medium light intensities (200 and 1000 lx) than under the highest intensity (5000 lx). In contrast, during the PL stage, growth was not strongly affected by photoperiod but was significantly greater ( p < 0.001) at 5000 lx than at 200 or 1000 lx. Although the optimal photoperiod and light intensity differed markedly among developmental stages, survival was not significantly affected by the light environment. In behavioural experiments using a projector to generate different light intensities, larvae at the ZM stage showed strong positive phototactic behaviour ( p < 0.05), whereas this behaviour was weaker at the PL stage. These results suggest that kuruma shrimp growth during the ZM stage is enhanced under photoperiods including a dark phase and low-to-medium light intensities. Overall, our findings suggest that the optimal photoperiod and light intensity for M. japonicus shift during development: light regimes including a dark phase and low to medium intensities may favour early larval growth, whereas high light intensity enhances growth at later stages.