This study focused on the influence of body size of teleosts on tolerance and the implications in a predator and prey relationship. Body size limitations are evident in many predator and prey relationships and as a result there is the potential for variation in tolerance to hypoxia. It was predicted that prey would have a greater tolerance of hypoxia than its piscine predator. I suggested the difference in body size would account for this difference as some physiological evidence was found to supports this. Three physiological parameters, expected to increase in response to a reduction on dissolved oxygen, were measured in response to hypoxia and were used to determine tolerance. All of the physiological variables measured suggested a size sensitive relationship in which the smaller prey (fathead minnow, Pimephales promelas') was better able to withstand hypoxic conditions than the predatory yellow perch ('Perca flavescens'). Based on this size-sensitive relationship of tolerance to hypoxia, I developed a theoretical model based on the ideal free distribution to determine the distribution of a predator and prey population in response to fluctuating dissolved oxygen levels. (Abstract shortened by UMI.)