Abstract
The natural range of fish species in our rivers is related to flow, elevation, temperature, local habitat and connectivity. For over 2000 years, humans have altered to varying degrees the river habitat. In the past 200 years, we added to the environmental disruption by discharging poorly treated sewage, nutrients and industrial waste into our rivers. For many rivers, the low point arrived during the period of 1950s–1970s, when rapid economic development overrode environmental concerns and dissolved oxygen concentrations dropped to zero. In these more enlightened times, gross river pollution is a thing of the past in the Developed World. However, persistent legacy chemical contaminants can be found in fish long after their discharge ceased. Changes in habitat quality and morphology caused and continue to cause the disappearance of fish species. The range of fish stressors has now increased as temperatures rise, and non-native fish introductions bring new diseases. The threat from pharmaceuticals to fish populations remains hypothetical, and no studies have yet linked change in fish populations to exposure.
Highlights
The exploitation of rivers in the developed Western world is considered to represent a high threat to biodiversity [1], and freshwater fishes are considered among the most threatened group of vertebrates worldwide [2]
Are there any messages to be inferred from studies on fish populations in proximity to sewage effluent, or those inadvertently exposed to the highest concentrations of pharmaceuticals during low flows? Roach populations do well in warm summers, which might be considered to be periods of low flows [14,15]
From what we can understand of our river history, the biggest catastrophes, where fish were wiped out en masse, were related to gross industrial and human waste pollution frequently causing oxygen depletion, and so these factors were ranked highest in the figure
Summary
The exploitation of rivers in the developed Western world is considered to represent a high threat to biodiversity [1], and freshwater fishes are considered among the most threatened group of vertebrates worldwide [2]. This review focuses on the challenges faced by fish in the river environment and tries to put pharmaceuticals in that context. European fish species have preferences for a wide diversity of conditions from cold, fast flowing, highly oxygenated water at one end to warm, slow and low oxygen conditions at the other [5]. The diversity of species along river networks appears to largely conform to differences in temperature, flow and habitat [7,8,9]. There are increasing attempts to use fish to help assess the ecological status of rivers, such as with the ‘European fish index’ (FBI, fish-based index) [10]
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