ABSTRACT
Water reservoirs have been constructed in hot semi-arid regions, which may be used to produce fish. The present study described major features of the economic, social, and environmental characteristics of a net-cage Nile tilapia production system, stocked with 100 and 120 fish/m3, implemented in a reservoir in the hot semi-arid region of Brazil during an extended drought event. The production cycle was reduced from 6-8 to 4 months because of the lack of water in the reservoir. This resulted in the harvest of small fish weighting ~300-350 g that reached a low value in the market. As a consequence, indicators of financial feasibility showed low values, which were not attractive for entrepreneurs. Nevertheless, for both stocking densities, the monthly income was about US$ 1,500.00, which is 5-fold the minimum wage in the region. In general, the activity has a positive social impact, despite the low contribution to development of the local economy and food security because most supply came from outside and fish were sold to distant regions. Various age and ethnic groups were represented among the employees, but the enterprise was operated only by men. Phosphorus accumulations in the reservoir were 2.1 and 2.0 kg/t of fish produced and particulate material accumulations of 110 and 100 kg/t of fish production for 125 fish/m3 and 100 fish/m3, respectively. The study indicated that the Nile tilapia culture in hot semi-arid region is strongly affected by long drought events and adaptations in the planning and management should be done when implementing the systems. However, it seems that the activity has some resilience to still provide food, generate wealth, and promote social development for local population with low environmental impact.
Subject(s)
Cichlids , Animals , Aquaculture , Droughts , Agriculture , Phosphorus , WaterABSTRACT
ABSTRACT: Continental aquatic ecosystems play a fundamental role in economic and social development; however, they are vulnerable to environmental degradation due to the various stresses to which they are submitted. Aquaculture is among the main anthropic activities that influence these environments. Mathematical modelling of aquatic ecosystems performed using a set of computational tools allows simplified representation of environment regarding its biotic and abiotic components. Some of the most used techniques are: hydrodynamic modelling, focusing on the dispersion of nutrients; nutrient-mass balance modelling, especially phosphorus; bioenergetic modelling in animal production systems, with an estimate of the generation of residues in the environment by farmed animals; and trophic and ecological modelling, focusing on aquatic communities and their interactions. These techniques help understand changes caused by aquaculture systems in aquatic environments. In this way, it is possible to estimate the magnitude and extent of the impacts of these activities by simulating the possible environmental changes over time. It can be concluded that techniques involving mathematical modelling can provide relevant information for future impacts prediction on aquatic environments, promoting the management of water resources and their multiple uses.
RESUMO: Ecossistemas aquáticos continentais desempenham papel fundamental no desenvolvimento econômico e social, entretanto, são vulneráveis à degradação ambiental devido às diversas pressões a que estão submetidos. Entre as principais atividades antrópicas a interferir nestes ambientes, podemos destacar a aquicultura. A modelagem matemática de ecossistemas aquáticos permite a representação simplificada do ambiente, em seus componentes bióticos e abióticos, através de um conjunto de ferramentas computacionais. Neste contexto, entre as técnicas mais utilizadas estão a modelagem hidrodinâmica, com foco na dispersão de nutrientes; a modelagem do balanço de massa de nutrientes, em especial o fósforo; a modelagem bioenergética em sistemas de produção animal, com estimativa da geração de resíduos pelos animais de cultivo para o ambiente; e a modelagem trófica e ecológica, com foco nas comunidades aquáticas e suas interações. Estas técnicas auxiliam no entendimento das alterações provocadas por sistemas de aquicultura em ambientes aquáticos. Deste modo, é possível estimar a magnitude e extensão dos impactos destas atividades, simulando as possíveis alterações ambientais ao longo do tempo. Pode-se concluir que as técnicas envolvendo modelagem matemática podem produzir informações relevantes para a predição de impactos futuros sobre ambientes aquáticos, dando subsídios para a gestão de recursos hídricos e seus múltiplos usos.