Fish growth and degree-days I: selecting a base temperature for a within-population study

Degree-days (DD) are an increasingly popular method for explaining variation in fish growth and development. By including a base temperature (T-o) the DD formula limits calculations T-o temperatures that are relevant T-o growth. However, our review of growth studies shows multiple T-o values in use for a given fish species. T-o determine how T-o affects the ability of DD T-o explain within-population growth variation, we first show that the ability of DD T-o describe a growing season is robust T-o low values of T-o. We then analyze immature length data from eight species and 85 water bodies in North America T-o show that there is a broad range of T-o values that effectively explain growth variation. Based on these results, we argue that precise T-o estimates are unwarranted for most single-population studies and recommend standard T-o values (0, 5, 10, 15 degrees C). Standardization facilitates comparative studies and promotes the use of DD in future research. To this end, we provide equations for converting annual DD at a given T-o to annual DD at a standard T-o.