Consumption of particulate wastes derived from cage fish farming by aggregated wild fish. An experimental approach

Particulate wastes derived from cage fish farming are a trophic resource used by wild fish. This study assesses waste consumption by wild fish and the impact on the final balance of wastes. Consumption was determined according to the difference between the particulate matter exiting the cages and that reaching 5 m away at three different depths, in the presence and absence of wild fish. Wild fish around the experimental cages were counted during feeding and non-feeding periods. A weighted abundance of 1057 fish 1000 m−3 consumed 17.75% of the particulate wastes exiting the cages, on average. Consumption was higher below the cages, where waste outflow was greater. However, waste removal by wild fish was noteworthy along the shallow and deep sides of the cages. Wild fish diminished the net particulate wastes by about 14%, transforming them into more easily dispersible and less harmful wastes. This study demonstrates the mitigating potential of wild fish in reducing environmental impact.This research was funded by the Spanish Institute of Agro-Forestry Research (INIA; Ministry of Economy and Competitiveness; project RTA2011-00088-00-00). The study was also partially sponsored by the student grant sub-programme for researcher training, of the Spanish Institute of Agro-Forestry Research (FPI-INIA)