Photoperiod is a key environmental indicator for regulating embryonic development,individual growth and physiological processes in aquatic animals.In this study,differences in embryonic development and performance of newly hatched cuttlefish juvenile exposed to five different cycles of light:dark(L:D):constant light,18L:6D,12L:12D,6L:18D cycles,and constant darkness were evaluated.Prolonged exposure to light induced an accelerated rate of embryonic development,particularly after the red-bead stage.Principal component analysis(PCA)revealed that red-bead stage,heartbeat,endoskeleton formation,pigment appear,and six increments of cuttlebone were the main factors contributing to the embryonic development.Meaning that the duration time of these five stages were significantly different when exposed to photoperiod regimes,which may determine the duration of the incubation period of the embryos.Long term light has also affected the incubation parameters with an increased rate in hatching and shortened the incubation and hatching periods in the 12-24-h day length range.However,constant light and darkness environment appeared to have a greater effect on the stress of embryonic development,mainly reflected in the yolk shed ratio and the inking rate in the egg capsule.Moreover,the increase in the day length has contributed to improve the growth and survival of juveniles in the 12-18-h day length range;however,juveniles exposed to constant light and darkness experienced worse results in terms of growth,tissue glycogen content,digestive enzymes of the digestive glands,and metabolic enzymes of the muscles.These finding suggest that prolonged light exposure accelerates the process of embryonic development,maximum feeding time is not necessarily a condition of optimal growth,and inappropriate light cycles can disturb the body's endogenous controls.Therefore,the optimal photoperiod for the embryos development and juvenile growth of Sepia pharaonis were 12 h and 12-18 h of day length,respectively.These results are useful for increasing the production of this species during embryo incubation and juveniles rearing in aquaculture practice.

Key Laboratory of Applied Marine Biotechnology,School of Marine Sciences,Ningbo University,Ningbo 315211,China

[1]Maowang JIANG;Huan CHEN;Shuangnan ZHOU;Qingxi HAN;Ruibing PENG;Xiamin JIANG-.Changes in embryonic development,juvenile growth and physiological adaptation of the cuttlefish Sepia pharaonis in response to photoperiod manipulation)[J].海洋湖沼学报（英文版）,2022(05):2012-2027

cuttlefish,pharaonis,endoskeleton,cuttlebone,inking

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