Survival data for dewatered Rainbow Trout (Salmo gairdneri Rich.) eggs and alevins

Survival of four intergravel development phases of rainbow trout, Salmo gairdneri Rich., in a dewatered environment varied with stage of development, duration of exposure, and relative humidity. Egg phases were considerably more tolerant than alevin phases. Cleavage eggs tolerated dewatering for 12 consecutive days (97% survival), the maximum period tested. Embryos tolerated dewatering until they began hatching on the eight day, when mortalities sharply increased. In contrast, eleutheroembryos had only 43% survival when dewatered 6h and pre-emergent alevins had only 36% survival when dewatered 2h. A few dewatered embryos died when relative humidity was 100%, but mortality increased significantly at 90 and 80% relative humidity. Survival of alevin phases, but not egg phases, in residual, non-flowing water was limited by formation of oxygen deficits.