title: Does CO2 enhance short-term storage success of Chinook salmon (Oncorhynchus tshawytscha) 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% O2 being the most common method. Salmonid sperm maintained in a storage environment with elevated carbon dioxide (CO2) levels, such as the approximately 4% 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-free oxygenated environment. Therefore, the effect of CO2 (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 CO2-exposure with subsequent CO2 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 CO2 and O2 levels at 3 to 4 degrees C for up to 14 days. Milt samples were then removed from the incubation environments and maintained under CO2-free humidified air with continuous mixing for 4 h at 10 degrees C before analysis of motility. The resultant motility of samples incubated under 3.5% or less CO2 was not different than controls during the 14 d incubation period; motility of samples stored under higher CO2 tensions were significantly lower. The motility of samples incubated under 3.5% CO2 reached the maximum recovered motility after 2 h exposure to CO2-free humidified air, while the motility of sperm incubated under 13.4% CO2 levels recovered no motility even after 6 h exposure to CO2-free humidified air. The motility of samples incubated under normoxia was significantly greater than that of samples incubated under hyperoxia (approximately 90% O2) at both 7 and 14 d, regardless of the CO2 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 CO2 and that storage under hyperoxia negatively affects sperm function compared to storage under normoxia.
authors.affiliation: Department of Cell and Developmental Biology, The University of North Carolina at Chapel Hill, 27599-7090, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Bencic
authors.forename: R L
authors.initials: RL
authors.lastname: Ingermann
authors.forename: J G
authors.initials: JG
authors.lastname: Cloud
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000009:adverse effects*; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry / Q000662:veterinary; D005456:Fluorescent Dyes / Q000737:chemistry; D008297:Male; D017683:Oncorhynchus / Q000502:physiology*; D010100:Oxygen / Q000494:pharmacology; D012662:Semen Preservation / Q000379:methods / Q000662:veterinary*; D013081:Sperm Motility / Q000187:drug effects / Q000502:physiology; D013094:Spermatozoa / Q000187:drug effects* / Q000502:physiology
chemical_list: D005456:Fluorescent Dyes; D002245:Carbon Dioxide; D010100:Oxygen