Does Co 2 enhance short-term storage success of chinook salmon ( [formula omitted]) milt?

Abstract

Successful short-term storage of salmonid milt depends on numerous factors, including temperature, fluid volume, and gaseous environment, with storage at low temperatures under an atmosphere of 100% O 2 being the most common method. Salmonid sperm maintained in a storage environment with elevated carbon dioxide (CO 2) levels, such as the ∼4% CO 2 in exhaled air, are not motile when activated. While these modest levels of CO 2 inhibit sperm motility, the effect is reversible within hours after exposure to a CO 2-free oxygenated environment. Therefore, the effect of CO 2 (as a component gas in the storage environment) on chinook salmon ( Oncorhynchus tshawytscha ) sperm motility and viability was examined. The hypothesis of the current investigation was that CO 2-exposure with subsequent CO 2 removal would be beneficial during short-term chinook salmon milt storage. Milt samples were collected from mature (adult) and precocious (jack) male chinook salmon and stored under various CO 2 and O 2 levels at 3 to 4°C for up to 14 days. Milt samples were then removed from the incubation environments and maintained under CO 2-free humidified air with continuous mixing for 4 h at 10°C before analysis of motility. The resultant motility of samples incubated under 3.5% or less CO 2 was not different than controls during the 14 d incubation period; motility of samples stored under higher CO 2 tensions were significantly lower. The motility of samples incubated under 3.5% CO 2 reached the maximum recovered motility after 2 h exposure to CO 2-free humidified air, while the motility of sperm incubated under 13.4% CO 2 levels recovered no motility even after 6 h exposure to CO 2-free humidified air. The motility of samples incubated under normoxia was significantly greater than that of samples incubated under hyperoxia (∼90% O 2) at both 7 and 14 d, regardless of the CO 2 level. Sperm viability was relatively unaltered by any of the incubation conditions examined. The results of this investigation suggest that there is no apparent advantage to storage of chinook salmon sperm in the presence of CO 2 and that storage under hyperoxia negatively affects sperm function compared to storage under normoxia.