Qualidade da água e táxons fitoplanctônicos em sistemas agroecológicos de cultivo de peixes

Abstract

The water resources existing on the planet are currently used by man in different ways, one of them for the practice of fish farming, that is, for the cultivation of fish in nurseries. The water quality of the crop is essential for the good growth and development of the fish, as it also influences the communities of autotrophic organisms present in the cropping systems, such as phytoplankton. Several factors influence water quality and the occurrence of phytoplankton in fish farms, including the type of feed used. In this sense, the objectives of this work were to evaluate the water quality and the occurrence of phytoplanktonic taxa in fish culture nurseries submitted to two feeding treatments, one using pelleted feed and the other extruded. The water samples were obtained from subsurface nurseries for six months in 2014 and 2015. Physical variables (temperature and transparency) and chemical variables (pH, conductivity, dissolved oxygen, phosphorus and total nitrogen, total dissolved phosphorus, orthophosphate, ammonium), according to standard analytical procedures for water analysis. It was also carried out the survey of the phytoplankton taxa occurring in the nurseries in each sampled month and treatment. It was found a better water quality in the treatment with extruded ration and higher occurrence of taxa in treatment with pelleted ration and at the end of the experimental period. 21 taxa were identified: 13 are of the class of Chlorophyceae, followed by 6 of Euglenophyceae, 1 of Cryptophyceae and 1 of Coscinodiscophyceae. The classes Chlorophyceae and Euglenophyceae were the most representative, due to their adaptive strategies.