How Temperature Affects Early Life Stages of a Model Fish Species, Fathead Minnow: Impacts on Development, Sex Ratios, and Physiological Responses

Unfavorable water temperature during early life can lead to dramatic population-level consequences for fishes.  We conducted three experiments designed to identify how the magnitude and frequency of temperature variability affects early life stages in a model species, Fathead Minnow.  Treatments consisted of fluctuations of Δ8°C over either 12 or 24 hours, fluctuations of Δ4°C over 12 hours, and three constant temperatures (minimum, mean, and maximum of the fluctuations).  Our first experiment evaluated survival and developmental rates of embryos and larvae among the temperature treatments.  The second experiment explored the potential physiological mechanisms allowing fish to tolerate temperature fluctuations by comparing gene expression of two heat-shock proteins from embryos collected periodically during the thermal cycles.  Finally, we explored how temperature fluctuations affect sex ratios by raising larvae in the temperature regimes for 45 days.  We determined sex ratios using histology to identify phenotypic sex at day-45 and compared this to the genetic sex of each individual, based on the presence of a sex-linked genetic marker, to determine the degree of sex reversal caused by temperature fluctuations.  Understanding how temperature variability affects early life stages will be increasingly important as climate change is expected to increase thermal variability in many aquatic systems