Guidance for selecting base temperatures when using degree-days in fish growth analyses

Abstract

Degree-days (DD) are a useful metric for describing the thermal scope for fish growth and other physiological processes, but there is a lack of advice about how to calculate DD for a given fish species. In particular, appropriate values for the base temperature for growth ( T0) are unknown for most fish species. Previous work showed that inappropriate T0 values can bias growth rate estimates and lead to erroneous conclusions when comparing growth among populations. It is therefore critical to use biologically relevant T0 values when calculating DD. We used two approaches that leverage empirical growth data and bioenergetics models to estimate T0 for 82 fish species. We found that T0 varied among species and across thermal guilds, with coldwater species having relatively low T0 values and warmwater species having higher T0 values. In addition, T0 varied across life stages and depended on whether one selected air or water temperature data to calculate DD. We provide guidance for calculating DD in fish science for many species and scenarios.