Sperm quality analysis of normal season (NG) and out-season by photoperiod manipulation (PG) of male rainbow trout broodstock (Oncorhynchus mykiss).

Sperm quality parameters in rainbow trout (Oncorhynchus mykiss) were investigated during normal season spawning (November-January) and out-season spawning (July-August) treated with artificial photoperiod manipulation. Normal spawning males (n = 15) were kept in an open concrete pond under natural condition. Out-season spawning males (n = 15) were treated with artificial LED light (50 lm/m) in a closed concrete pond. In these two experimental groups, five fish were used in each of three spawning periods. The mean weight and body length of males (2 + years, n = 30) were 1213.43 ± 39.43 g and 45.08 ± 0.62 cm, respectively. Sperms were collected from July to August 2016 in the out-season spawning or photoperiod-manipulated group (PG) (water temperature 14.21 ± 0.31 °C) and from December 2016 to January 2017, in the normal season spawning group (NG) (water temperature 8.81 ± 1.03 °C). Volume of sperm, osmolality of seminal plasma, density of sperm, percentage of motile spermatozoa (MOT), curvilinear velocity (VCL), and duration of motility were measured for each male. Seminal plasma osmolality, density of sperm, and the motility of duration were 358.47 ± 37.24 and 308.87 ± 44.09, 4.37 ± 2.10 and 9.8 ± 1.56, and 8.8 ± 2.42 and 24.6 ± 6.76 in PG and NG, respectively. Fertilization rate was 37.79 ± 9.37% and 94.51 ± 1.33% in PG and NG, respectively. Sperm quality parameters showed significant differences in most of the cases (p < 0.05) and fertilization rate at eyed egg stage (150-160 degree-days) was significantly higher in normal season spawning group than the photoperiod-manipulated group (p < 0.05). Though the rate of fertilization was low in out-season, it was able to get enough gametes in summer using only artificial light having no changes in other parameters.