Effect of increased embryonic temperature during developmental windows on survival, morphology and oxygen consumption of rainbow trout (Oncorhynchus mykiss)

Temperature is a crucial environmental factor that influences physiological functions in fishes, and increased temperature during development can shape an organism's phenotype. An active line of inquiry in comparative developmental physiology is whether short-term exposure to thermal changes have lasting phenotypic effects. This is the first study to apply a developmental 3-dimensional critical window experimental design for a vertebrate, using time, temperature, and phenotypic response (i.e., variables measured). Rainbow trout (Oncorhynchus mykiss) are an anadromous species for which resident populations occupy freshwater environments that are likely impacted by variable and rising temperatures, particularly during embryonic development. To assess thermal effects on fish development, we examined trout hatchling phenotypes following rearing in constant temperatures (5, 10, 15 and 17.5 degrees C) and following exposure to increased temperature above 5 degrees C during specific developmental windows. Time to 50% hatch, hatchling mass and body length showed general trends of decreasing with increasing constant temperature, and survival was highest in constant 10 degrees C incubation. Thermally shifting embryos into 17.5 degrees C during gastrulation and organogenesis reduced survival at hatch compared to 10 degrees C, and exposure to 15 and 17.5 degrees C only late in development produced lighter and shorter hatchlings. Oxygen consumption rate (Vo(2)) at organogenesis differed between embryos incubated constantly in increased temperature or exposed only during organogenesis, but generally we found limited temperature effects on Vo(2) that may be due to high data variability. Collectively, these results suggest that survival of rainbow trout hatchlings is most sensitive to 17.5 degrees C exposure during gastrulation and organogenesis, while warm water exposure later in development has greater impacts on morphology. Thus, trait-specific critical windows of thermal sensitivity exist for rainbow trout embryos that alter the hatching phenotype.