Thermal preference does not align with optimal temperature for aerobic scope in zebrafish (Danio rerio)

Warming is predicted to have negative consequences for fishes by causing a mismatch between oxygen demand and supply, and a consequent reduction in aerobic scope (AS) and performance. This oxygen and capacity limited thermal tolerance (OCLTT) hypothesis features prominently in the literature but remains controversial. Within the OCLTT framework, we hypothesised that fish would select temperatures that maximise their AS, and thus their performance. We tested this hypothesis using intermittent flow respirometry to measure AS at, above (+2.5°C) and below (–2.5°C) the self-selected, preferred temperature (T(pref)) of individual zebrafish (Danio rerio). AS was greatest 2.5°C above T(pref), which was driven by an increase in maximal metabolic rate. This mismatch between T(pref) and the optimal temperature for AS suggests that factor(s) aside from AS maximisation influence the thermal preference of zebrafish.