Fish are more fearful in cloudy conditions

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Cloudy water makes marine fish less active and more fearful of predators, according to a study by Susannah Leahy and coauthors to be published in a forthcoming issue of the journal Biology Letters.

Conducting a series of experiments on the Spiny damselfish (Acanthochromis polyacanthus), the authors found that increasing the turbidity of the water reduced activity levels of the fish by 23%.

The authors observed a single damselfish in each of nine treatments repeated 20 times per treatment. In the nine treatments, the fish were exposed to one of three stimuli while their behaviours were recorded: seawater control, Swordtail (Xiphophorus helleri) skin extract and damselfish skin extract under one of the three water conditions (clear water, low and high turbidity).  

The authors found that the damselfishes spent half as much time foraging when exposed to conspecific alarm cues (from the skin extracts) under high turbidity conditions compared to either clear or low turbidity conditions.  

This implied that the damselfish was increasing its reliance on chemical input to assess risk of predation in situations where visual information was limited.

For more information, see the paper: Leahy, SM, MI McCormick, MD Mitchell and MCO Ferrari (2012) To fear or to feed: the effects of turbidity on perception of risk by a marine fish. Biology Letters doi:10.1098/rsbl.2011.0645

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