Globally, rivers are increasingly being subjected to various levels of physical alteration and river regulation to provide humans with services such as hydropower, freshwater, flood control, irrigation and recreation. Although river regulation plays an important role in modern society, there are potential consequences which may negatively affect fish and fish habitat. While much effort has been expended examining the response of fish to fluctuating flow regimes in different systems, there has been little in the way of a comprehensive synthesis. In an effort to better understand the effects of river regulation on fish and fish habitat, we conducted a systematic review of available literature with three goals: (1) summarize the various research methodologies used by regulated river researchers, (2) summarize the effects found on fish and fish habitat and (3) identify opportunities for future research. The results of the synthesis indicate that a wide variety of methodologies are being employed to study regulated river science, yet there is a gap in incorporating methodologies that examine effects on fish at a cellular level or those techniques that are interdisciplinary (e.g. behaviour and physiology). There is a clear consensus that modified flow regimes in regulated rivers are affecting fish and fish habitat, but the severity and direction of the response varies widely. Future study designs should include methods that target all biological levels of fish response, and in which detailed statistical analyses can be performed. There is also a need for more rigorous study designs including the use of appropriate controls and replicates. Data on physical variables that co-vary with flow should be collected and examined to add explanatory power to the results. Increased multi-stakeholder collaborations provide the greatest promise of balancing ecological concerns with economic needs.

The social experiences of individuals can influence their mate-choice decisions. Mate-choice copying is considered to have occurred if an individual's observation of a sexual interaction between a male and a female increases its likelihood of subsequently preferring the individual observed mating. Although such copying behaviour has been documented extensively in the laboratory, there exists only very limited evidence for its occurrence in nature. Here, we experimentally investigated female mate-choice copying in a wild Trinidadian population of the guppy (Poecilia reticulata), a species that exhibits such copying behaviour in the laboratory. Using a pair of Plexiglas tanks placed in situ in a river in Trinidad, we presented free-ranging adult females with a binary choice of viewing and affiliating with either of two similar-sized stimulus males: one male was viewed next to a visible model (demonstrator) female and the other male viewed apparently alone (placed next to a pseudo-model female hidden from the subject females). Focal subject females preferred to associate with the stimulus male that was near and consorting with a model female than with the lone stimulus male. The results of a separate control experiment suggest that this observed female preference was sexual in nature rather than a simple shoaling response. We conclude that our results are consistent with mate-choice copying behaviour and suggest that female guppies can mate-choice copy in the wild when given the opportunity, as they do under laboratory conditions.