Effect of Activated Milt Residence Time on Landlocked Fall Chinook Salmon Egg Survival

Abstract

During artificial spawning of salmonids, activated sperm is allowed to remain in contact with eggs for variable durations. This study examined multiple residence times (20, 40, 60, 90, or 120 seconds) for activated sperm on landlocked fall Chinook salmon (Oncorhynchus tshawytscha) eggs during spawning. There was no significant difference in egg survival to the eyed-stage of development or to hatch among any of the treatments, with a mean (SE) percent survival to the eyed stage of 63.9 (5.8). These results indicate that only relatively short residence times of activated milt on eggs during landlocked fall Chinook salmon spawning are needed to ensure egg survival, resulting in potentially substantial reductions in production-level spawning times and associated labor costs.

Effects of Two Activated Milt Residence Times on Landlocked Fall Chinook Salmon Egg Survival to the Eyed Stage of Development

“…The results of this study indicate that activated milt residence times for fall Chinook Salmon in Lake Oahe can be reduced to as low as 20 s without affecting egg survival, which is even less than the 30‐s residence time that was used successfully by Burrows (1949). These results also validate results from the small‐scale experiment reported by Shannon et al (2020). The lack of effect of such short milt residence times is not unexpected.…”

“…One 50‐mL tube of milt was split between the two egg containers, followed by 1 L of lake water (8°C; total hardness as CaCO 3 = 220 mg/L; alkalinity as CaCO 3 = 160 mg/L; pH = 8.2; total dissolved solids = 440 mg/L) to initiate fertilization (Barnes and Cordes 1992). After the addition of lake water to the milt and eggs, two activated milt residence times were used (one for each container of eggs): 20 and 60 s. Longer milt duration times were not used because this experiment occurred during actual production spawning when time was at a premium and Shannon et al (2020) found no difference in egg survival between 60 and 120 s. At the end of each treatment, the eggs were immersed in lake water for approximately 10 s to rinse excess milt from them (Piper et al 1982). After rinsing, the eggs were placed in a 3.79‐L plastic bag containing approximately 1 L of lake water, placed in a cooler, and allowed to water harden for approximately 1 h (Hayes and Armstrong 1942).…”

“…However, Reese et al (2017) observed spermatozoa motility ranging from 29 to 76 s in Chinook Salmon from the Lake Oahe population, which is considerably lower than the standard recommendation for residence time. Using a small‐scale experimental procedure, Shannon et al (2020) reported no significant difference in survival among eggs from Lake Oahe population that were subjected to residence times ranging from 20 to 120 s. Shannon et al (2020) also noted that using a 20‐s milt residence time during spawning, instead of the 120‐s standard, would result in substantial labor savings.…”

“…Because egg depth, milt concentration, and the amount of water that is used during actual spawning are different than those that are used to produce the small‐scale experimental results of Shannon et al (2020), the applicability of the Shannon et al (2020) study to production‐scale spawning was uncertain. Thus, this study was undertaken to verify the small‐scale experimental results of Shannon et al (2020) at a production level, using ratios of milt, eggs, and water that were similar to those that are used during actual spawning.…”