Effect of Different Photoperiod Regimes on Sperm Quality, Fecundity and Fertilization in Rainbow Trout (Oncorhynchus mykiss)

The present study was carried out to determine effect of different photoperiod regimes on sperm quality parameters, ovulation/spermiation time and hatchery performance of rainbow trout (Oncorhynchus mykiss) broodstock. The designation was done as combination of different long and short photoperiod regimes such as: 18L:6D and 18D:6L (group I); 14L:10D and 14D:10L (group II) and natural lighting (control group). All treatments were carried out as three replications at each group. As a result, the highest mean spermatozoa motility (83.0±2.1 %) and motility period (67.2±6.3 s) were determined in control group. It was determined that the longest ovulation was occured in female rainbow trout broodstock at 265 days in group I. Although the highest mean absolute egg productivity was determined as 3654.7±298.3 eggs/fish in group I, the highest mean relative egg productivity was determined as 137.3±24.5 eggs/kg in control group. Furthermore, the highest mean egg diameter (4.6±0.1 mm) and fertilization rate (87.0±2.5 %) were determined in control group. Statistical analyses revealed that spermatozoa motility, spermatozoa motility period and spermatozoa density positively correlated with fertilization rate in all photoperiod regimes (P>0.05). On the other hand, semen volume and semen pH negatively correlated with fertilization rate in all photoperiod regimes (P>0.05). It is interesting to note that only statistically important positive correlation was determined between relative fecundity and fertilization rate in 18L:6D/18D:6L photoperiod regime (r=0.452, P<0.05). Consequently, results revealed that combined long and short artificial photoperiod regimes can advance ovulation and spermiation and also can effect gamete quality and hatchery performance of rainbow trout during out-of-season spawning.