Temperature preference of brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) - an experimental study

Abstract

Invasive alien species threaten native ecosystems by outcompeting native species or by negatively altering the function of the natural ecosystem. In Sweden, the invasive brook trout (Salvelinus fontinalis) displace native brown trout (Salmo trutta) from their food and habitat niches. Because salmonids are ectothermic, water temperature is a critical factor for their survival. Generally, brook trout is more frequently detected in upper stretches of watercourses with colder water. The aim of this study was to investigate the thermal preferences of both species and determine whether a difference exists under a controlled laboratory setting. A temperature preference annuli (TPA) was used, allowing the fish to select their position along a thermal gradient. A weighted temperature index was calculated to represent individual temperature preference. The result indicated a significantly lower temperature preference for brook trout compared to brown trout (p = 0.027). Furthermore, there was a statistically significant interaction between body condition and species on the weighted temperature index (p = 0.037), this indicates that how the body condition impacts temperature preference differs between species. Additionally, diurnal temperature preference was more variable for brook trout than for brown trout as water temperature increased. Overall, brook trout had a more varied temperature preference than brown trout, suggesting a higher phenotypic plasticity and individually based choices. This study provides fundamental data for future research. These findings contribute to a better understanding of brook trout and brown trout ecology in Sweden, informing conservation efforts, brook trout management and ecosystem responses to climate change.