Hypoxia and fish: ecological and evolutionary consequences

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Over the past century, freshwater ecosystems have suffered as a result of intense human modification, with devastating consequences for fish biodiversity. Of the many challenges facing freshwater fishes is the increasing occurrence of oxygen scarcity in the water (hypoxia). While low levels of dissolved oxygen (DO) occur naturally in waters characterized by low light and low mixing (e.g., swamps), hypoxia is becoming more widespread as influx of wastes and fertilizers accelerates eutrophication and pollution. It is therefore increasingly important to understand the consequences of low-oxygen stress on fish populations. This research program aims to (1) understand the ecological and evolutionary consequences of hypoxic stress for fishes, and (2) apply this understanding to current conservation and management issues. We focus on inland waters of East Africa where hypoxia is widespread and problems of biodiversity conservation are acute. By comparing fish populations that cross DO gradients and rearing fish under different DO conditions, we can detect changes in the morphology, physiology, and behaviour in response to hypoxic stress. In the Lake Victoria basin of East Africa, hypoxic stress has increased associated with severe eutrophication. Changes in water quality of the lake in conjunction with introduction of the predatory Nile perch has led to the extinction of many endemic fishes. This project also investigates changes (morphological, physiological) in remnant species that may have fostered their persistence in the face of environmental change.