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Abstract Human-induced noise has a pervasive influence on the behaviour of animals in their natural environment, but little scientific attention has gone toward noises that regularly affect animals being maintained in captivity for research purposes. Here, we assessed underwater aquarium noise produced from two types of aeration equipment (an airstone diffuser attached to an air pump vs. aeration from a mounted aquarium filter) and used recordings from a hydrophone to characterize these two noise stimuli. For several months, we maintained fathead minnows, Pimephales promelas, in a laboratory environment with aeration and noise from an airstone. Then minnows were moved into tanks with either the familiar airstone noise or novel filter noise for four days. We then measured the latency of minnows to emerge from an isolation chamber as a standard measure of boldness behaviour. Exposure to novel filter noise resulted in decreased boldness (P