<p>Diet is a key physiological factor shaping brain function and gut microbiota, which together form the dynamic gut-brain axis. This bidirectional communication system plays a pivotal role in regulating behavioural outcomes. Therefore, it is worth investigating various behavioural aspects and connecting them with gut microbial dynamics shaped by differential dietary composition. Using zebrafish, we examined the effects of monotypic and combined diets of live feed and commercial feed on behavioural outcomes, morphometry, and gut microbiota. After chronic dietary intervention, fish receiving a mixed diet (Artemia, pellet, and spirulina) showed behavioural profile with enhanced exploration, reduced anxiety-like behaviour, and moderate aggression, alongside a balanced gut microbial composition. In contrast, monotypic diets produced distinct effects: Artemia-only fish displayed reduced boldness, heightened anxiety, and pathogenic microbial enrichment, while pellet-only fish showed greater growth but increased aggression. These findings highlight the importance of mixed feeding regimens for maintaining healthy gut-brain-behaviour interactions and support zebrafish as a model for studying diet-microbiota-behaviour relationships.</p>