What can go wrong for future Senegalese sole recruitment? Temperature and food availability as important drivers of early-life-history traits.

Water temperature and prey availability are key factors influencing the successful recruitment of early life stages in fish. Understanding how these variables modulate larval growth and survival is essential for modelling larval dynamics. In this study we reared S. senegalensis larvae under controlled laboratory conditions to assess the effects of temperature and feeding frequency on larval development. Three temperatures (17, 20, and 23 °C) and three feeding frequencies (Ff 2.5 fed 2.5 times per week, Ff 4 four times per week, and Ff 6 six times per week) were tested from 12 to 32 days post-hatch (dph) in both individual and group housing systems. Survival, growth, and metamorphosis progress were monitored, and the expression of six genes related to nutrition (tryp1a and apoA4Aa2), cellular stress (hsp90aa and hsp70), endocrine regulation (tgb), and muscle development (myf4) were monitored on S3 and S4 metamorphic larvae. The feeding frequency appeared as the primary driver influencing all investigated traits, while temperature played a less pronounced effect. These data demonstrate the critical role of energy provision in regulating growth, development, and survival, which interacts with temperature, particularly under conditions where metabolic and energy demands cannot be fully fulfilled. Additionally, the Senegalese sole larvae exhibited compensatory genomic adaptive responses to efficiently mobilize nutrients from the gut and adjust the thyroid axis and cellular responses to support metamorphosis transformation and metabolism when food availability was limited or when temperature approached physiological thresholds.