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K. Mueller, S. C. F. Neuhauss; Simple Behavioral Assay for Testing Vision of Adult Zebrafish and Medaka. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1435.
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Zebrafish and medaka both have emerged as potent model organisms for studying development, including the development of visual function. A multitude of behavior based visual tests are established for larvae that have been successfully used to identify and characterize visual defects in genetically manipulated fish strains. Testing the visual system of adult fish has proven to be more difficult for a number of reasons, including complications in restraining fish, or shoaling and dominance behavior interfering with visual behavior in population screening assays.
Our method is based on the larval optokinetic response (OKR) assay. Measuring the optokinetic response of larval zebrafish is well established: larvae can be immobilized by embedding in methylcellulose, and their dark pigmented eyes, clearly silhouetted against the transparent body, can easily be recognized and tracked by computer programs.To restrain body movements of adult fish, we employed a custom-made flow-through chamber in which the body of the fish was gently clamped between two pieces of sponge, leaving the head with the eyes and gills free and in direct contact with water. Fish restrained by this method were calm enough to measure a stable OKR for prolonged periods, making it possible to measure several paradigms (e.g. contrast sensitivity, temporal and spatial resolution) successively.Shading body pigmentation through overlay of virtual white triangle images enabled reliable tracking of the eyes.
We made use of this technique to compare the optokinetic response of adult zebrafish and medaka. Contrast sensitivity and temporal resolution of these species turned out to be very similar, whereas medaka showed a significantly lower spatial resolution than zebrafish. In addition, saccade frequency is higher in medaka. Both species show a stronger response to motion stimuli in the temporal to nasal direction.
The OKR assay is a simple, robust and cost-effective method for testing visual performance of adult fish. Because of the short time involved in handling and testing, the method could even be used as a tool to screen for mutations affecting the adult visual system.
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