| Summary: | This study was conducted to assess the effects of photoperiod on growth and spawning of zebrafish. Two hundred and forty zebrafish (120 males and 120 females) were maintained under four different light dark cycles: shortened light regime (08L:16D), control (12L:12D), extended light regime (16L:08D), and continuous light regime (lights on continuously for 24 h). The fish were kept in these conditions for 42 days, during which growth and reproduction were measured. The best growth was achieved at the ELR group, with the greatest final mean weight (P < 0.05). Zebrafish cultured in 24L:00D produced significantly more larvae than those in 08L:16D at 34th days (P < 0.05). A higher hatching rate was observed in 16L:08D compared to the other groups (P < 0.05). The percentage of ovulated zebrafish females was significantly higher in 16L:08D than in the other groups (P < 0.05). The outcome indicates that extending day length affects both growth and spawning of zebrafish. Together, these data suggest that a photoperiod of 16L:08D might be optimal for laboratory zebrafish, at least from a production standpoint.
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