Effects of spectral composition,photoperiod and light intensity on the gonadal development of Atlantic salmon Salmo salar in recirculating aquaculture systems(RAS)

Artificial lighting regimes have been successfully used to inhibit sexual maturity of Atlantic salmon in confinement.However,when these operations are applied in commercial recirculating aquaculture systems(RAS) using standard lighting technology,sexual maturation is not suppressed.In this study,an L_9(3~3) orthogonal design was used to determine the effects of three factors(spectral composition,photoperiod,and light intensity) on the gonadal development of Atlantic salmon in RAS.We demonstrated that the photoperiod at the tested levels had a much greater effect on the gonadosomatic index and female Fulton condition factor than spectral composition and light intensity.The photoperiod had a significant effect on the secretion of sex steroids and melatonin(P<0.05),and a short photoperiod delayed sex steroid and melatonin level increases.The three test factors had no significant effects on the survival rate,specific growth rate,relative weight gain,and male Fulton condition factor(P>0.05).The optimum lighting levels in female and male Atlantic salmon were LD 8:16,455 nm(or 625 nm),8.60 W/m^2;and LD 8:16,8.60 W/m^2,455 nm respectively.These conditions not only delayed gonadal development,but also had no negative effects on Atlantic salmon growth in RAS.These results demonstrate that a combination of spectral composition,photoperiod and light intensity is effective at delaying the gonadal development of both male and female salmon in RAS.

Extent of mismatch between the period of circadian clocks and light/dark cycles determines time-to-emergence in fruit flies

Circadian clocks time developmental stages of fruit flies Drosophila melanogaster, while light/dark （LD） cycles delimit emergence of adults, conceding only during the ＂allowed gate.＂ Previous studies have revealed that time-to-emergence can be altered by mutations in the core clock gene period （per）, or by altering the length of LD cycles. Since this evidence came from studies on genetically manipulated flies, or on flies maintained under LD cycles with limited range of periods, inferences that can be drawn are limited. Moreover, the extent of shortening or lengthening of time-to-emergence re- mains yet unknown. In order to pursue this further, we assayed time-to-emergence of D. rnelanogaster under 12 different LD cycles as well as in constant light （LL） and constant dark conditions （DD）. Time-to-emergence in flies occurred earlier under LL than in LD cycles and DD. Among the LD cycles, time-to-emergence occurred earlier under T4-T8, followed by T36-T48, and then T12-T32, suggesting that egg-to-emergence duration in flies becomes shorter when the length of LD cycles deviates from 24 h, bearing a strong positive and a marginally negative correlation with day length, for values shorter and longer than 24 h, respectively. These results suggest that the extent of mismatch between the period of circadian clocks and environmental cycles determines the time-to-emergence in Drosophila.