Does CO2 enhance short-term storage success of chinook salmon (Oncorhynchus tshawytscha) milt?

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 ca rbon dioxide (CO2) levels, such as the similar to4% CO2 in exhaled air, are not motile when activated. While these modest levels of CO2 inhibit sperm motility, the effect is reversible within hours after exposure to a CO2-fre e oxygenated environment. Therefore, the effect of CO2 las a component gas in the storage environment) on chinook salmon (Oncorhynchus tshawytscha) sp erm motility and viability was examined. The hypothesis of the current inve stigation was that CO2-exposure with subsequent CO2 removal would be benefi cial during short-term chinook salmon milt storage. Milt samples were colle cted from mature (adult) and precocious (jack) male chinook salmon and stor ed under various CO2 and O-2 levels at 3 to 4 degreesC for up to 14 days. M ilt samples were then removed from the incubation environments and maintain ed under CO2-free humidified air with continuous mixing for 4 h at 10 degre esC before analysis of motility. The resultant motility of samples incubate d under 3.5% or less CO2 was not different than controls during the 14 d in cubation period; motility of samples stored under higher CO2 tensions were significantly lower. The motility of samples incubated under 3.5% CO2 reach ed the maximum recovered motility after 2 h exposure to CO2-free humidified air, while the motility of sperm incubated under 13.4% CO2 levels recovere d no motility even after 6 fi exposure to CO2-free humidified air. The moti lity of samples incubated under normoxia was significantly greater than tha t of samples incubated under hyperoxia (similar to 90% O-2) at both 7 and 1 4 d, regardless of the CO2 level. Sperm viability was relatively unaltered by any of the incubation conditions examined. The results of this investiga tion suggest that there is no apparent advantage to storage of chinook salm on sperm in the presence of CO2 and that storage under hyperoxia negatively affects sperm function compared to storage under normoxia. (C) 2001 by Els evier Science Inc.