A REVISED MODEL OF VISUAL RANGE IN FISH

opportunities and predation risk in the pelagic habitat. We compare an earlier published model with measurements of the reactive distance of Gobiusculus flavescens relative to two species of copepods. Although this model gave reasonable predictions at low light intensities, the m easurements of reactive distance at higher intensities were much lower than those predicted by the model. We modified the model to account f or saturation at high light intensities. With this additional feature, the correspondence with the G. flavescens observations was significan tly improved. Furthermore, the revised model is consistent with earlie r published data on fish contrast thresholds obtained over a wide ran of target sizes and irradiance levels. Given the values of only two pa rameters, one sensitivity threshold and one saturation parameter, the model is capable of predicting visual ranges for relatively large inte rvals of light intensity, prey size and turbidity. Other published vis ual range models are briefly reviewed and compared with our model.