Impact of control of the golden mussel on the production costs of tilapia bred in net cages
Impacto do controle do mexilhão-dourado no custo de produção de tilápia em tanques-rede
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The economic impact of the control of the golden mussel on tilapia bred in net cages, with different volumes and production scales, is evaluated. Twelve fish farms were selected in Ilha Solteira Reservoir, on the Paraná River (between the states of São Paulo and Mato Grosso do Sul), and in the Canoas II and Chavantes Reservoirs on the Paranapanema River (between the states of São Paulo and Paraná), Brazil. A semi-structured questionnaire provided data on expenditure and capital required for calculating control costs. Expenses on labor, maintenance and depreciation of infrastructure and equipments, cage maintenance, additional depreciation and costs with electricity or fuel for cleaning were accounted. Large-size enterprises had the lowest costs, regardless of net cage volume. Cage depreciation and maintenance greatly influenced costs for mussel control, reaching an average rate of 69.89%. Lowest added costs were reported in large-size fish farms (R$ 0.45 kg fish-1), followed by medium- and small-size ones (R$ 1.00 kg fish-1). Mean economic impact reached 11.48% (large-size), 27.25% (medium-size) and 25.81% (small-size). Impact varied between 7.83% and 19.22%, respectively, in 108m3 and 6m3 net cages.