An Original Investigation of the Neurobiology of Stress Responses and Their Implications for Welfare and Productivity in Intensively Farmed Catfish in Nigeria

Fish welfare is an emerging concern in Nigerian aquaculture that has received almost no scientific attention, despite its potential significance for both ethical animal husbandry and practical production outcomes including growth, disease susceptibility, and product quality. This study makes an original contribution to understanding stress response neurobiology and its production implications in intensively farmed Clarias gariepinus through a combination of neuroendocrine profiling, behavioural observation, gene expression analysis, and production performance measurement under standardised and commercial farming stress scenarios. Stress scenarios investigated included crowding stress at five stocking densities, transport stress simulation, handling during sampling, and chronic feed restriction. Cortisol and glucose concentrations, measured by ELISA from non-lethal blood sampling, served as primary stress biomarkers. Brain gene expression of corticotropin-releasing factor, glucocorticoid receptor, and serotonin transporter genes was quantified by RT-qPCR. Behavioural indicators of chronic stress were video-recorded and scored using an original catfish welfare behavioural assessment protocol developed as part of this study. Results demonstrated that stocking densities above 80 kg/m3 produced persistent cortisol elevation (greater than 120 ng/mL) associated with 17% reduced growth rate and a threefold increase in ectoparasite burden over 12 weeks. The study introduces the catfish welfare behavioural assessment protocol as an original validated welfare measurement tool for intensive Nigerian catfish farms and provides neuroendocrine evidence supporting stocking density limits of 60 kg/m3 as a welfare-based production guideline for Clarias gariepinus in intensive systems.

Keywords: fish welfare, stress response, cortisol, Clarias gariepinus, intensive aquaculture