Development of a larval fathead minnow optomotor response assay for assessing visual function

The optomotor response (OMR) is a position stabilizing reflex to whole-field visual motion, demonstrated by fish instinctually moving to follow alternating black and white stripes. The OMR assay is used to assess the visual function of fish. While researchers have been using the OMR assay for years to evaluate the visual acuity of fish, no standardized methods exist. Therefore, the goal of the present study was to develop a standardized protocol for the measurement of OMR in larval fathead minnows, a common model species in ecotoxicology. Results indicate that OMR is a potential endpoint for the assessment of vision in larval fathead minnows and can be quantified as early as 9 dpf. When running the OMR assay, a 4-min acclimation period should be implemented. There did not appear to be a learning component to response latency; however, high variation in likely impeded the ability to detect significant differences. • Optomotor response of fathead minnow larvae can be quantified as early as 9 dpf. • When running the assay, a 4-min acclimation period should be implemented. • Due to high variation, response latency is not recommended for use as an endpoint.