Wild fish associated with tropical sea cage aquaculture in South Sulawesi, Indonesia

Abstract This study investigated wild fish diversity adjacent to floating fish cages used for the culture of groupers, Epinephelus fuscoguttatus and Cromileptes altivelis, and rabbitfish, Siganus spp., in South Sulawesi, Indonesia. Wild fishes were significantly more abundant in near-surface depths around the margins of the cages in the morning than at other times of day, and corresponding to the time when the fish within the cages were fed with formulated diets. There were 29 species of wild fishes, belonging to 25 genera, associated with the cages. Of these, 5 species were observed feeding on pellets passing through the cage: Abudefduf vaigiensis, Pterocaesio tile, Monodactylus argenteus, Neopomacentrus violascens and Sphaeramia orbicularis. The total biomass of wild fishes outside the cages exceeded the biomass of aquacultured fishes. Aggregations of wild fishes outside the cages consumed a total amount of organic material equivalent to that of the uneaten food leaving the cages, and directly consumed 27% of the lost pellets, significantly reducing organic waste from the cages. The trophic impact of wild fishes should be considered when assessing the effects of sea cages on the surrounding environment.

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