Effects of wild fishes on waste exportation from a Mediterranean fish farm

ABSTRACT: This study investigated the role of wild fishes associated with marine farms as potentialconsumers of organic waste in the water column and sediment. Experiments were carried out at a fishfarm in a semi-enclosed bay in the Mediterranean Sea (SE Spain). Sediment traps collected organicwaste from net-pens in the water column at different depths during June and July 2001 and benthiccaging experiments were carried out on the sediment from October 2000 to January 2001. Theexperiment showed that about 80% of the particulate organic matter leaving the rearing net-pensmay be consumed before it settles on the sediment. Significant changes in the nutrient quality of theorganic matter exported are also due to consumption by wild fishes. Wild fishes thus play an impor-tant role in recycling the organic matter of the sediment, and regulate the benthic community struc-ture. Our results indicate that the trophic role of wild fishes should be considered when evaluatingthe environmental impact of fish farms.KEY WORDS: Aquaculture · Wild fishes · Fish farm · Sea-cage · Organic waste · Mediterranean Sea