Effects of music enrichment on the welfare of small ornamental fishes

Auditory enrichment is an emerging method to enhance the welfare of ornamental fish, yet its effects remain poorly understood. This study evaluated how music style and tempo influence stress-related behaviors and cortisol secretion in two model species: zebrafish (Danio rerio) and guppies (Poecilia reticulata). Fish (n = 4 × 3 per species) were exposed for five consecutive days (4 h/day) to one of four auditory treatments—slow-tempo piano (SP, 40–65 bpm), fast-tempo piano (FP, 150–210 bpm), slow-tempo guzheng (SG), fast-tempo guzheng (FG)—or to silence (control). Positive behaviors (touching the water surface, following, wandering) and negative behaviors (freezing, aggression, sprinting) were quantified from 15-min video recordings. Whole-body cortisol concentrations were measured using ELISA. Music enrichment significantly affected both behavioral responses and cortisol levels (ANOVA, p < 0.05). In zebrafish, SP and SG promoted positive behaviors, whereas FP and FG increased negative behaviors; SG alone significantly lowered cortisol relative to the control. In guppies, FP, SG, and FG increased positive behaviors; SG reduced negative behaviors; and all music treatments significantly decreased cortisol levels. Novel tank test performance was unaffected in either species. Overall, slow-tempo guzheng music exerted the strongest anxiolytic effect, particularly in guppies. We conclude that playback of slow guzheng music offers a practical, non-invasive approach to reduce stress and improve welfare in ornamental fish housed in barren aquaria.