Acclimation Improves Short-Term Survival of Hatchery Lahontan Cutthroat Trout in Water From Saline, Alkaline Walker Lake, Nevada

We investigated the effectiveness of two acclimation protocols for 8-month-old Lahontan cutthroat trout Oncorhynchus clarkii henshawi, reared at Lahontan National Fish Hatchery in terms of survival during a week-long challenge in water from saline, alkaline Walker Lake, Nevada. Fish were acclimated for 0 (control), 3, and 8 d by increasing the ratio of lake water to hatchery water. For the 3-d acclimation treatment, 50% of the tank water was replaced with lake water each day. For the 8-d treatment, 33% of the water was replaced with lake water on the first through fourth day of acclimation. Survival during acclimation (i.e., prior to the challenge) was lowest for fish acclimated 3 d. Median survival time during the lake water challenge was 8 h for unacclimated fish, and 8 and 12 h for fish surviving the 3- and 8-d acclimation treatments, respectively. No fish survived the entire week-long challenge. Compared with no acclimation, 3- and 8-d acclimation decreased the hazard of mortality during the challenge. Increased fork length also reduced the hazard of death. Our results indicate acceptable survival rates cannot be achieved for subyearling, hatchery-reared Lahontan cutthroat trout stocked in Walker Lake without acclimation or with the acclimation methods employed in this study. Our results indicate that the acclimation method might be improved by the use of longer fish, longer acclimation, and better control of water temperature, ammonia concentration, and alkalinity.