Effect of photoperiod manipulation on the growth performance of juvenile lenok, Brachymystax lenok (Pallas, 1773)

Abstract

Summary The effect of four different light regimes on growth was studied in lenok, Brachymystax lenok. Fish with average weights of 5.5 g were subjected to four different photoperiods (0L:24D, 6L:18D, 12L:12D and 24L:0D) for 35 days. The specific growth rate (SGR) of lenok in 24-h darkness had a significantly higher SGR than those in the continuous light regime (P < 0.05); however, there was no significant difference among fish exposed to 6L:18D, 12L:12D and 24L:0D photoperiods. There was a tendency for higher food intake over the light period extension from 0L to 24L, and feed intake was significantly higher in the continuous light group than in 24-h darkness (P < 0.05). No significant difference in feed conversion efficiency (FCE) was observed between fish exposed to 0L:24D and 6L:18D photoperiods, however, the FCE in both photoperiods was significantly higher than that in the other two groups. The final survival rate of juveniles varied from 79.67 to 95.33%, with significant differences among experimental groups. Fish tested in continuous illumination spent much more energy on respiration and excretion while depositing less energy for growth than in the other photoperiods. In contrast, fish in 24-h darkness deposited more energy for growth and spent less energy on respiration and excretion. Results show that photoperiod manipulation can affect growth, and that a continuous dark regime could improve growth in lenok at this stage of development.