Engin, S., 2022. The first commercially-scaled study on the influence of long dark and light photoperiod manipulation on the egg and larvae performance of rainbow trout (Onchorhynchus mykiss). Journal of Coastal Research, 38(1), 196–203. Coconut Creek (Florida), ISSN 0749-0208.

Spawning success, number of eyed-egg, and larval growth performance of rainbow trout are largely affected by a variety of biotic and abiotic factors. The photoperiod is important in initiating or suppressing breeding timing and gonadal maturation that varies by species. The aims of this study were to investigate the effect of two different commercial photoperiod manipulations on the growth of total eyed eggs, egg diameter, and larvae under specific fish farm conditions. The control group (outdoor broodstock ponds and natural sunlight) fish were fed using a commercial broodstock feeding protocol in September and transferred to the hatchery in February for spawning. The female and male broodstocks were exposed to direct photoperiod (Experimental Group 1: M1), and for the adapted photoperiod (transition from light to dark periodically, Experimental Group 2: M2) they were exposed to 18 hours of light and 6 hours of darkness between January and April. The M1 group were exposed to a direct application of 18 hours of dark and 6 hours of light, and a transition from light to dark for 18 hours and from dark to light for 6 hours was applied to M1 that was completed over 48 days with a daily decrease of 17 minutes. The results of the trials showed that larval growth was higher in the groups treated with long light and long dark, 18 hours light/6 hours dark and 18 hours dark/6 hours light compared to the control group, and statistically significant difference between larval survival rate and daily weight gain was observed between all three groups (p < 0.05). As a result, at the end of the photoperiod, applications and larvae breeding performed for one year under commercial operating conditions were compared, and larvae with higher survival and growth rates were obtained with long light and long dark application.