Increases in cortisol production facilitate the transition to exogenous feeding by larval zebrafish

The transition to exogenous feeding is a critical developmental period that is regulated by corticosteroids in mammals. However, mechanistic evidence linking corticosteroids with feeding transitions in non-mammalian vertebrates remains scarce. Here, we pharmacologically suppressed cortisol production during the period preceding exogenous feeding by larval zebrafish (Danio rerio) and determined how this influenced feeding rates and transcript levels of digestive enzymes. Water-borne metyrapone (an 11β-hydroxylase inhibitor) from 3-5 days post-fertilization (dpf) blocked the 2-fold rise in cortisol levels observed in control larvae during this period. While whole-animal growth and development were unaffected, cortisol synthesis suppression during this period resulted in lower transcript abundance of digestive enzymes and reduced feeding rates at 5 dpf. However, these differences dissipated following a two-day washout period. Together, our results indicate that cortisol influences feeding transitions in zebrafish, highlight the plasticity of these processes following perturbations, and suggest that this mechanism is conserved across vertebrates.