Coral reefs are among the most biodiverse ecosystems in the oceans, harbouring 25% of all known marine species. Amongst the hubbub of biogenic noise, fish contribute significantly to the cacophony of reef sounds. However, with 25% of the human population living on the worlds coastlines, coral reefs are experiencing unprecedented change. Using wild orange-fin anemonefish (Amphiprion chrysopterus) female–male adult pairs (Moorea, French Polynesia), this thesis aims to: 1) explore the in situ natural vocal repertoire of A. chrysopterus, and 2) test for impacts of light pollution on diurnal behaviour. Previous studies assessing anemonefish acoustic communication and the influence of artificial light at night (ALAN) on anemonefish behaviour are predominantly laboratory-based. For the first time, by assessing in situ vocal behaviour using a single-pulse analytical approach, this research found new layers of complexity in Amphiprion communication. Orange-fin anemonefish were found to: i) infrequently engage in acoustic communication unless exposed to a ’rival’ conspecific, ii) show sex- based differentiation in pulse peak frequency, iii) vary substantially in pulse peak frequency within and between pulses and iv) diverge from the previously-reported relationship between fish size and pulse frequency. Following in situ exposure to IMMEDIATE (one night) and PROLONGED (14–35 nights) exposure to ALAN (~12–26 lux), subsequent diurnal behaviour of female anemonefish was not significantly influenced. In contrast, male behaviour was significantly altered, but only following long-term exposure. This research deepens our understanding of anemonefish vocal behaviour and demonstrates that male and female anemonefish have differing responses to the stressor of light pollution; important in developing mitigation for fishes in sex-structured social groups. Overall, this thesis showcases anemonefish as a valuable model species for in situ fieldwork, with the methodologies developed here proposed as being easily-adapted to assess the effects of other stressors on fish behaviour in this rapidly-changing world.