Metal pollution poses significant risks to human health, aquatic life, and ecosystems. While individual metals such as iron (Fe), manganese (Mn), and cadmium (Cd) are known to affect fish development and behavior, the impact of metal mixtures at environmental concentrations remains underexplored. This study investigates the effects of these metals, individually and in combination, on the early development and behavior of zebrafish. It evaluates parameters, such as mortality rates, hatching success, growth, and stress indicators. The metals were tested at concentrations found in a river in the Minas Gerais state of Brazil. Exposure to individual metals caused disruptions in developmental and behavioral markers in zebrafish larvae, with the order of toxicity being Cd > Mn > Fe. Specifically, reductions in somite count, heart rate, locomotor activity, and thigmotaxis were observed, particularly in fish exposed to Cd and Mn. Interestingly, an increase in locomotor activity was noted in fish exposed to Fe. When the metals were mixed, they still affected developmental markers but did not significantly alter the behavioral responses of the larvae. Markers of the stress response, such as levels of protein, glucose, and cortisol, showed no significant changes following exposure to either the individual metals or their mixtures. Overall, the metal mixture demonstrated a synergistic effect on developmental markers, amplifying the impacts produced by the individual metals, while exhibiting an antagonistic effect on behavioral markers, thereby reducing the changes observed with individual metal exposures. This indicates that fish may exhibit distinct early developmental responses in environments impacted by metal mixtures.