Environmental manipulations for captive Lahontan cutthroat trout increase hatchery egg survival and survival of yearlings stocked in saline, alkaline Walker Lake, Nevada

I investigated the reproductive temperature requirements of captive Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) brood females, and various acclimation protocols for yearling, hatchery-reared Lahontan cutthroat trout stocked in saline, alkaline Walker Lake, Nevada Survival of eggs to the eyed developmental stage, hatching, and yolk-sac resorption was higher when spawned from brood females held in chilled water (7.2°C) from mid December through spawning compared to eggs spawned from females on ambient well water (12.4°C) regardless of whether females were spawned 0, 4, or 7 d post ovulation. Female holding temperature did not appear to affect the timing of ovulation however, fecundity was higher for females held at 7.2°C versus 12.4°C. The hazard of mortality during a week-long challenge in water from Walker Lake, Nevada for eight-month-old Lahontan cutthroat trout reared at Lahontan National Fish Hatchery was lower for fish acclimated 3 and 8 d by gradually increasing the ratio of lake water to hatchery water compared to un-acclimated fish. Increased fork length also reduced the hazard of death. No fish survived the entire week-long challenge, indicating improvements in the acclimation method are necessary. In a second acclimation study, the hazard of mortality for yearling, hatchery-reared Lahontan cutthroat trout during three replicate week-long challenges in saline, alkaline water from Walker Lake was lower for fish acclimated for 17 d at the hatchery in simulated lake water than for un-acclimated fish however, acclimation for 8 d seemed to have no effect. Fish condition factor and fork length were directly correlated to challenge survival. Blood plasma osmolality was elevated in fish not surviving the challenge however, challenge survivors that had been acclimated for 17 d exhibited normal plasma osmolality. These results will facilitate the recovery of Lahontan cutthroat trout in the Truckee-Tahoe and Walker subbasins.