Biotratamento em piscicultura: avaliação da sua eficácia com bioindicadores

Abstract

Fish and other aquatic resources are relevant for human feeding, due to the availability of proteins, however, fishing is an activity that increasingly contributes less to the supply of fish, due to overfishing and water body pollution. To compensate for this, there has been a huge increase in aquaculture activities, including fish farming. This can be a great incentive for social and economic development, but like other economic activities, it can be potentially harmful for the environment. The cultivation of fish in ponds produces the release of residues and metabolites that are the main cause of water enrichment, due to the feeding and excretion of the animals. These dissolved or suspended substances initiate eutrophication process, causing a series of modifications in the water environment and, consequently, on its biotic communities, thus leading to the reduction of water quality, which as a consequence decreases fish production. In eutrophized ponds or mesh tanks, fishes can accumulate cyanotoxins when cyanobacteria are the dominant group in the phytoplankton. To avoid / delay the eutrophication processes, a bioremediation treatment was tested, using biofilm as a sustainable alternative to prevent eutrophication in fish farming tanks. To analyze the effectiveness of biotreatment, monitoring with bioindicators (zooplankton community) was carried out. Plastic modules were installed for colonization by the biofilm in excavated tilapia breeding nurseries in the municipality of Camalaú, in the semi-arid region of Paraíba. From November 2016 to March 2017, water samples were collected from the ponds for evaluation of zooplankton community composition, both in the presence (treated) or absence (control) of the bio-treatment. Results obtained demonstrated the efficacy of biotreatment, with the presence in higher densities of species that indicate lesseutrophized environments in the nurseries treated with biofilm, such as the species Ceriodaphnia cornuta (cladocera) and calanoida (copepod). The highest densities of species that indicated eutrophic environments were found in the control nurseries, such as Moina minuta and Alona dentifera (cladocera). Among the rotifers, the species Brachionus urceolaris, B. calyciflorus, B. havanaensis and Hexarthra mira and the cyclopoid (copepod) are indicative of eutrophic environments. Bioremediation and the use of biological indicators contributed to the improvement of the water quality of the nurseries. This was reflected in the production of fish, which showed greater growth and weight in the ponds with biofilm.