The Effects of Capture and Transportation Stress on White Bass Semen Osmolality and Their Alleviation via Sodium Chloride

Abstract

White bass Morone chrysops were captured by hook and line from the Illinois River and transported for 5 h in either freshwater or water with 5‰ NaCl; they were then maintained in separate water reuse systems at their respective salinities. Blood plasma osmolality, semen osmolality, and semen motility were monitored for 57 h. Our objectives were to determine whether semen dilution could be induced by capture, handling, and transportation stressors, and to determine if sodium chloride would alleviate the expected stress-induced decreases in blood plasma and semen osmolality. White bass transported and held in freshwater had lower mean (±SE) plasma osmolality at 30 h (263 ± 17 mosmols/kg) and 44 h (269 ± 13 mosmols/kg) compared with the initial plasma osmolality (330 ± 4 mosmols/kg). Mean semen osmolality for the white bass (312 ± 8 mosmols/kg) decreased at 30 h (273 ± 6 mosmols/kg) and 44 h (251 ± 7 mosmols/kg). Semen osmolality paralleled blood plasma osmolality over time in each treatment. Plasma and semen osmolality in the 5‰ NaCl treatment group increased at 30 h due to the excess addition of NaCl to the culture system water; otherwise, there were no significant changes in either plasma or semen osmolality in the saltwater group. Spermatozoa showed motility prior to activation with water in 38% of the freshwater treatment semen samples, which on average exhibited 10–25% motile cells. In contrast, we observed no sperm motility prior to activation in the 5‰ NaCl treatment group. Stress-induced dilution appeared to have caused in vivo semen dilution and premature activation of the spermatozoa in the freshwater treatment group. Transporting and holding white bass in 5‰ NaCl alleviated osmoregulatory distress and also promoted survival; 93% of the NaCl-treated white bass survived, compared with 30% in the freshwater treatment. We demonstrated that changes in semen osmolality, as well as premature sperm activation, correspond to stress-induced changes in blood plasma osmolality. Semen osmolality may be useful as a stress indicator.