The rainbow runner (Elagatis bipinnulata) and the oceanic triggerfish (Canthidermis maculatus) are two of the main bycatch species of the FAD-based tuna purse-seine fisheries in the world. Within the framework of an ecological based management, baseline information of these species is required to assess the ecosystem impacts of tuna fisheries. To date, little information is available on the basic biology and behaviour of those two species. Acoustic telemetry on fish associated with FADs (57 oceanic triggerfish and 26 rainbow runners) provided information on their associative behaviour. Additionally, biological sampling on fish caught by purse seiners was used to investigate the diet of both species.