Establishing Zebrafish as a Model for Acute Pain: Behavioral and Cellular Responses to Acetic Acid Exposure

The zebrafish ( Danio rerio ) is emerging as a valuable vertebrate model for nociception research due to its genetic homology with humans, cost-efficiency, and amenability to high-throughput behavioral analysis. However, data on chemically induced acute pain and associated physiological responses in adult zebrafish remain limited. This study examined behavioral and hematological responses to waterborne acetic acid (AA) at 2.5%, 4%, and 5% concentrations. Behavioral responses, including swimming speed, distance travelled, and movement trajectories, were analyzed using video tracking, while peripheral blood smears were assessed for leukocyte morphology. Exposure to 4% and 5% AA significantly increased locomotor activity and elicited erratic trajectories (p < 0.05), indicative of nocifensive behavior. At 5% AA, a reduction in spatial exploration suggested behavioral suppression at higher noxious intensities. Blood analysis revealed elevated leukocyte counts, particularly monocytes, in the 5% group, reflecting an inflammatory response. This study presents a novel, non-invasive model for inducing and quantifying acute pain-like states in adult zebrafish. These findings support the use of zebrafish in pain mechanism research and open new avenues for screening analgesics and anti-inflammatory agents under ethically favorable conditions.