Zooplankton forms the bulk of its diet. Small crustaceans and fish larvae are taken opportunistically. It feeds on drifting prey caught in current while hovering above reef structures. The demoiselle is a small blue-green fish that lives in rocky reefs and kelp forests throughout New Zealand. It reaches about 120 millimetres in length, with a streamlined body adapted to life in currents. The fish is coloured bright blue-green with darker edges on scales, creating a shimmering effect in sunlight. Large schools form above reef structures, moving as one entity to confuse predators. The species inhabits shallow coastal waters from the intertidal zone down to 30 metres depth. Rocky reefs and kelp forests provide shelter from predators and spawning sites during spring months. Without this structure, the fish becomes visible to everything that hunts it. The habitat is widespread along New Zealand's coastline, though local populations vary in density. Spawning occurs in spring and summer. Eggs are laid on rocky substrate in shallow water. The male guards the eggs, fanning them to keep oxygenated. The larvae hatch and drift in plankton before settling back onto reefs as juveniles. This pelagic larval stage allows dispersal between reef systems. Classified as Not Threatened, the demoiselle remains abundant throughout New Zealand. Populations are stable in suitable reef habitat. However the species is sensitive to water quality degradation. When reefs are damaged by sedimentation or pollution, populations decline rapidly. Its presence signals intact reef ecosystems and suitable water quality. Conservation efforts focus on protecting remaining reef habitats and maintaining water quality to keep coastal ecosystems healthy.