The effect of extended cold storage and the use of extenders on motility and swimming kinematics of shortnose sturgeon sperm

Shortnose sturgeon ( Acipenser brevirostrum ) are listed as a species of special concern in Canada and as endangered in the US. Increasing knowledge about the reproductive biology of this species will aid in the development of assisted reproduction protocols. However, access to wild sperm is limited, so short-term and long-term storage of sperm from sturgeon is crucial for reproductive studies. Milt samples were collected from wild shortnose sturgeon caught in the Wolastoq River, New Brunswick, Canada. Subsets of semen were mixed with different extenders with or without oxygen; control treatments without extenders were also run. We used computer-assisted sperm analysis (CASA) to determine sperm motility and swimming kinematics for the different treatments. All groups were examined immediately after collection and treatment application, and then 1, 2, and 7 days after storage in a fridge (4 o C) for experiment 1, and days 1, 3, 7, 10, 14, 17, 21, and 24 for experiment 2. Motility, curvilinear velocity, linearity, and wobble showed an overall decrease over time, and there was no significant effect of oxygen. Milt treated with the Park and Chapman extender had the slowest motility decline of extenders used (41.21% in 2022 and 47.09% in 2023) after 7 days, but only maintained motility up to day 10. While untreated milt maintained some motility up to day 21, milt treated with the modified Tsvetkova extender remained motile for up to 24 days (<5%), and had less potential for contamination, making the modified Tsvetkova extender the most practical extender choice. • Motility persisted up to day 21 without extenders and with or without oxygen. • The extenders Park and Chapman and modified Tsvetkova most prolonged motility. • Milt treated with the Park and Chapman extender showed slower decline of motility. • Milt treated with the modified Tsvetkova extender showed less visible contamination.