Otolith increments in common sole (Solea solea) reveal fish growth plasticity to temperature

Phenotypic plasticity is a major mechanism allowing organisms to respond to environmental variability. Understanding phenotypic plasticity of organisms to warming is crucial to predict future impacts of climate change. In this study, we investigated fish growth plasticity to temperature using a large archive of otoliths collected from 1960 to 2020, providing growth data over the period 1958-2019, of three common sole (Solea solea) populations: North Sea, Irish Sea, and Bay of Biscay. We used mixed-effects models to partition growth variation into its intrinsic (age, age at capture) and extrinsic (temperature, density, fishing pressure, nutrient) components; to disentangle individual-level plasticity from the population-level response to temperature; and to assess the environmental dependency of growth plasticity. We demonstrated that sole growth plasticity followed the Temperature-Size Rule with increasing juvenile growth and decreasing adult growth at higher temperature. Under favourable conditions for sole growth, the positive response to warming in juvenile fish is stronger while the negative response in adult fish is weaker and the individual plasticity variance is lower. Our study provides additional support for the universality of the Temperature-Size Rule and contributes to our understanding of fish populations' responses to current and future climate change.