Effects of Constant Temperature and Thermal Shifts on Survival, Morphology, and Oxygen Consumption in Rainbow Trout (Oncorhynchus mykiss) Embryos

Environmental temperature is a crucial environmental factor that influences many physiological functions in fishes. Rainbow trout (Oncorhynchus mykiss) are a native anadromous species that inhabit a variety of freshwater rivers and lakes and are widely distributed throughout the western portion of the United States. Resident rainbow trout populations occupy interior freshwater environments for the entirety of life. Interior bodies of water are most susceptible to changes in environmental temperatures. Therefore, resident rainbow trout are likely to be impacted by variable and rising temperatures, particularly during embryonic development. Understanding temperature effects during development is likely to provide insight into the overall thermal biology of a species and its persistence in a changing climate. To assess the effect of temperature on development of rainbow trout, we examined phenotypes of hatchery embryos reared in various incubation temperatures (5°C, 10°C, 15°C and 17.5°C). To identify the presence of embryonic developmental plasticity within developmental time points, embryos incubated in 5°C were exposed to either 10°C, 15°C or 17.5°C during gastrulation, organogenesis, system integration or growth windows and a 3-dimensional critical window model was applied. An increase in constant incubation temperature increased oxygen consumption rate (V̇O2), and decreased hatchling survival, mass, yolk size, body length and time to 50% hatch. Thermally shifting embryos into increased temperature during distinct windows of development also reduced survival at hatch, and this was most evident following exposure during organogenesis, which may signify the presence of a critical window for this trait. Likewise, thermally shifting embryos into increased temperature resulted in smaller hatchlings. Although there was an initial increase in V̇ O2 in response to temperature, experiencing thermal shifts during development had no persistent effect on V̇ O2 when measured at hatch at 5°C compared to 5°C constant embryos. Collectively, these results suggest that survival and morphological traits of rainbow trout embryos are most sensitive to increased temperature during organogenesis and system integration, but increased temperature does not appear to have a long-term effect on energy use. Environmental temperature plays a fundamental role in developing aquatic vertebrates. Thus, critical window studies such this performed across species will eventually allow for the identification of commonalities in plasticity between different species in response to variables such as temperature.