Several studies on fishes have shown that behaviour and auditory sensitivity are often affected by underwater noise. The current investigation concentrates on noise encountered by fish kept for leisure in aquaria and ponds. Noise spectra showed that all aquarium filters measured created a high amount of low-frequency noise, while the water outflow above the surface created additional high-frequency noise components. Audiograms of the Goldfish Carassius auratus, a species possessing hearing specializations, were determined between 0.1 and 4kHz using the noninvasive
auditory evoked potential (AEP) recording technique. The amount of masking was determined in the presence of four different noise-types: aquaria with external filter with outflow above the water surface (119dB re 1 µPa), external filter with outflow below the water surface (115dB), internal filter with outflow below the water surface (114dB broadband LLeq, 1min), and an unfiltered pond (95dB). The goldfish’s hearing was masked by all filter noise types and most affected at 0.1 and 0.3kHz by the external filter noise (threshold shifts of 15-19dB). Pond noise had no effect on the hearing threshold. The results indicate that fish with hearing specializations are considerably masked under common holding conditions found in aquaria but probably not in ponds. Thus, using a quieter filter setup with a quiet outflow might help to improve holding conditions in aquaria without compromising aeration of the water.