Psychobiotics in Aquaculture: Harnessing the Microbiome-Gut-Brain Axis for Stress Management and Production Enhancement in Fish.

Intensified aquaculture production has significantly increased farmed fish exposure to various stressors that compromise welfare and productivity, demanding innovative approaches to enhance sustainable production. Aquaculture environments subject fish to multiple stressors. These include high-density housing, handling, transportation, and fluctuating water quality. Such stressors activate the hypothalamic-pituitary-interrenal axis, resulting in a cascade of endocrine responses. This subsequently impairs feeding behavior, growth performance, and immune function. Psychobiotics exert beneficial effects by producing neuroactive compounds, including gamma-aminobutyric acid, short-chain fatty acids, serotonin, and dopamine. Key bacterial genera such as , , , and demonstrate significant psychobiotic properties. Experimental evidence from zebrafish and commercially relevant species demonstrates that psychobiotic interventions consistently reduce cortisol levels, normalize stress responses, and improve behavioral outcomes. These effects occur through the microbiome-gut-brain axis, a bidirectional system connecting the nervous and gastrointestinal systems by neural, endocrine, and immune pathways. Nevertheless, significant challenges persist, such as species-specific efficacy, limitations in mechanistic understanding, and the need for standardized evaluation protocols. This review examines psychobiotics as promising interventions for stress management in aquaculture systems. We conclude that psychobiotics may offer a sustainable approach for mitigating aquaculture stress responses and enhancing both fish welfare and production efficiency through targeted microbiome modulation.