Altered acoustic environments influence boldness in minnows

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 < 0.001), despite being weaker in sound intensity than the airstone noise, leading us to view the novelty of the sound as being representative of a novel environment with unknown threats for minnows. We then returned minnows to their previous noise environment or the opposite noise environment for an additional four days, finding that minnows reverted to bolder behaviour when returning to the familiar acoustic environment (airstone) (P = 0.035), whereas no acclimation to the novel noise environment (filter) occurred over the additional four days. Our results suggest that aquatic animals in laboratory studies deserve more attention in regard to the intensity and novelty of their acoustic environment.