Beyond the glass: testing visitor effects on the behavior of teleost fish in public aquaria

Abstract

Zoos and public aquariums serve as essential hubs for wildlife conservation, public education, and scientific research; however, the success of these missions depends upon maintaining high animal welfare standards despite constant human presence. A primary concern is the 'visitor effect': the modification of animal behavior due to human presence. While this phenomenon is well-documented in captive mammals and has been explored in Chondrichthyans, it remains largely unexamined in teleost fish, despite evidence of their sensitivity to human stimuli in natural environments. This study addresses this knowledge gap by investigating the behavioral responses of 13 teleost species to varying levels of visitor density, direct human solicitations, and ambient noise. Our multivariate analysis reveals that the total number of visitors present in the aquarium and the direct sonic human solicitations (such as knocking on the glass) are significant drivers of behavioral changes. We observed high inter-taxonomic variability: while Euxiphipops sextriatus, Dascyllus aruanus, Zebrasoma flavescens, Chaetodontoplus mesoleucus and Pygoplites diacanthus showed marked sensitivity through significant modifications in their behaviors the others (Amphiprion percula, Chaetodon rafflesia, Chromis viridis, Chrysiptera parasema, Heniochus chrysostomus, and Lactoria cornuta) showed no obvious behavioral changes. Furthermore, acoustic analysis indicates a complex soundscape where global visitor density correlates with increased sound amplitude, particularly in the 100 Hz to 400 Hz range, a critical band for teleost hearing, suggesting that visitor-induced noise is distinct from the aquarium's technical background noise (pumps, aerator etc). These findings underscore that the 'visitor effect' is not a uniform phenomenon but a complex interaction shaped by species-specific sensitivity and distinct anthropogenic actions. Our results highlight the necessity of incorporating species-specific behavioral data and acoustic monitoring into welfare management protocols to better mitigate the impact of human presence on captive fish populations.