Ocean warming drives tissue-wide metabolic reprogramming in a fish.

Ocean warming and marine heatwaves are predicted to have adverse impacts on marine organisms. Yet, knowledge of the molecular mechanisms that underpin successful or failed acclimation to increasing temperatures remains incomplete. We conducted an aquaria-based study of early-life stage clownfish comprising of six thermal regimes, measuring the metabolic, and multi-tissue transcriptional response of Amphiprion ocellaris using seven tissues. Sampling at 31°C increased metabolic rates in fish reared at 28°C; however, these effects were reduced with increasing developmental rearing at 31°C. Transcriptomic analysis revealed multi-tissue reprogramming of metabolic processes at +3°C, particularly in the liver-pancreas axis. Importantly, chronic larval-juvenile exposure to +3°C induced the acclimation of metabolic rates and caused the upregulation of oxidative phosphorylation (liver) and the downregulation of insulin secretion (pancreas). These results indicate that temperature increase will drive tissue-wide metabolic reprogramming in fish, with changes in key energetic pathways underpinning fish's ability to acclimate to warming.