Survival of Apache Trout eggs and alevins under static and fluctuating temperature regimes

Increased stream temperatures due to global climate change, livestock grazing, removal of riparian cover, reduction of stream flow, and urbanization will have important implications for fishes worldwide. Information exists that describes the effects of elevated water temperatures on fish eggs, but less information is available on the effects of fluctuating water temperatures on egg survival, especially those of threatened and endangered species. We tested the posthatch survival of eyed eggs and alevins of Apache Trout Oncorhynchus gilae apache, a threatened salmonid, in static temperatures of 15, 18, 21, 24, and 27°C, and also in treatments with diel fluctuations of ±3°C around those temperatures. The LT50 for posthatch survival of Apache Trout eyed eggs and alevins was 17.1°C for static temperatures treatments and 17.9°C for the midpoints of ±3°C fluctuating temperature treatments. There was no significant difference in survival between static temperatures and fluctuating temperatures that shared the same mean temperature, yet there was a slight difference in LT50s. Upper thermal tolerance of Apache Trout eyed eggs and alevins is much lower than that of fry to adult life stages (22–23°C). Information on thermal tolerance of early life stages (eyed egg and alevin) will be valuable to those restoring streams or investigating thermal tolerances of imperiled fishes.