Carbon dioxide reversibly inhibits sperm motility and fertilizing ability in steelhead (Oncorhynchus mykiss)

Abstract

The effects of different carbon dioxide (CO2) levels on the short-term storage of semen samples from hatchery-produced steelhead (Oncorhynchus mykiss) were evaluated. Sperm motility and fertilizing ability were significantly reduced following 4 h incubation under a relatively modest (≥0.9 kPa = 1%) amount of CO2. The dose-dependent reductions, however, were not the result of cell death as sperm viability was unaltered even at the highest (5.2 kPa = 5.6%) CO2 exposures. Reductions in sperm motility and fertilizing ability were reversible. Although previous work has indicated a direct relationship between salmonid sperm motility and sperm ATP content, the inhibitory effects of CO2 on sperm motility were not the result of reduced sperm ATP levels. Decreasing the pH of the seminal fluid (to below ∼7.5) significantly reduced sperm motility. However, this effect was only observed after prolonged (4 h) exposure; short-term (1 min) exposure to this lowered pH did not alter sperm motility. Moreover, acetazolamide, a carbonic anhydrase inhibitor, attenuated the inhibitory effects of CO2 on sperm motility. These results suggest that CO2 inhibits steelhead sperm motility and therefore fertility in a dose-dependent manner, by reversibly lowering intracellular pH.