Responses to light in terms of embryonic development and larval phototactic behavior in sea cucumber, Apostichopus japonicus

Apostichopus japonicus is an economically important species of sea cucumber and the rearing of larvae is a vital initial step in its culture. Light plays a nonnegligible role in the sea cucumber life cycle. However, few studies have investigated the optimal lighting conditions for embryonic development and the phototactic behavior of larvae. Thus, in this study, we examined the effects of different light color treatments (red, blue, and dark at 200 lx) on the body length, survival rate, and development speed of A. japonicus embryos. The results indicated that the light color did not affect the body length, but blue light delayed development and increased mortality, whereas red light promoted growth. Among five red light intensity treatments (50, 100, 300, 500, and 1000 lx), red light at 500 lx was optimal for development. Red light at both 50 lx and 100 lx did not have positive effects, and red light at 1000 lx inhibited growth. In addition, auricularia larvae exhibited negative phototaxis under red light at 500 lx. These results provide a theoretical basis for further studying the mechanism associated with the response to light in sea cucumbers and essential information for enhancing sea cucumber aquaculture techniques.