EFFECTS OF WINTER AND SUMMER THERMAL VARIABILITY REGIMES ON GROWTH AND METABOLISM IN BROOK TROUT (Salvelinus fontinalis)

Brook trout (Salvelinus fontinalis) is a cold-water species with a narrow range of thermal tolerance. Climate change projections show that in addition to increases in average temperatures worldwide, daily thermal variability is increasing. Such conditions could prove challenging for brook trout and other ectotherms that are adapted to small temperature ranges. This research investigates how the growth and metabolic capacities of brook trout respond to long-term exposure to thermal variation. Groups of fish were reared under three thermal regimes: constant baily temperature, a 4°C daily range, and an 8°C daily range in a controlled lab setting. This was completed once in the winter centered on 6°C, and once in the summer centered on 12°C. The mass and length of fish from each group was measured to assess growth rates, and blood was drawn to measure circulating cortisol levels. At the end of each treatment exposure series, fish from each group were subjected to swimming respirometry to assess metabolic and energetic capacities. The growth data showed no significant effect of the treatments in either season. Cortisol levels were elevated in response to temperature variability under winter conditions, but not during the summer conditions. Respirometry revealed no significant metabolic differences between treatment groups. These findings suggest that brook trout possess substantial resilience to increased thermal variability, but that the effects on cortisol levels are different under winter and summer conditions