Long‐Term Boat Noise Effects on Growth and Behavioural Patterns During Early Life Stages of the African Cichlid Maylandia zebra

Underwater anthropogenic noise is currently recognised as a global environmental pollutant, with negative impacts on the behaviour and physiology of a wide range of aquatic animals. However, long‐term studies on the effects of chronic exposure to anthropogenic noise on fish are lacking, especially regarding early life stages. Here, we focused on a well‐known fish behavioural model, the cichlid fish Maylandia zebra , to assess the effects of boat noise on early life stages over 12 weeks. To minimise potential genetic effects, a split‐brood approach was employed, with half of each female's offspring exposed to control treatment (100 dB re. 1 μPa), while the other half was subjected to boat noise treatment (120 dB re. 1 μPa). Subsequently, we closely monitored weekly changes in growth and behaviour, including foraging, territorial behaviour, swimming, and group cohesion. We found that juveniles exposed to boat noise exhibited increased foraging activity and swimming distance, stayed closer to the water surface, and showed reduced digging behaviour, shelter use, and group cohesion compared to control juveniles. However, at the end of the experiment, there were no differences between treatment and control fish in any measured variable, suggesting habituation to noise. Our findings suggest that long‐term boat noise affects a suite of behaviours during development that appear to change in concert—likely by the need to maintain an energy balance—and differ from those observed under short‐term noise exposure. These changes could pose unpredictable risks in the wild, especially before habituation occurs.