Avaliação da sanidade em cultivos de tilápia (Oreochromissp.): qualidade da água, alterações branquiais e identificação de espécies fúngicas

Abstract

The objective of this work was to evaluate the health of tilapia (Oreochromis sp.) crops through water quality, gill alterations and identification of fungal species. The collections were carried out in the metropolitan areas of São José de Ribamar and Paço do Lumiar, in the city of São Luís, state of Maranhão, Brazil, Water and thirty fish were collected to analyze the gills in six fish farms, three in São José de Ribamar (P1, P2 and P3) and three in Paço do Lumiar (P4, P5 and P6). The producers were interviewed from a semi-structured questionnaire to investigate, in particular, the management and sanity of the fish. The parameters were: hydrogenation potential (pH), temperature, salinity, dissolved oxygen (O.D.), ammonia and nitrite in situ in fish farms. Microbiological analyzes for determination of the Most Likely Number (MPN) of total coliforms and Escherichia coli were performed using the Colilert method. The gills and fish skin samples were removed for analysis of histological lesions and fungal isolation. The gills were removed and fixed in 10% formalin for 48 hours and for the preparation of the slides, the samples passed through histological processing. Isolation of the fungi from fish gills and skins samples was done in agaroud dextrose agar medium plus clorafenicol. Histological changes were assessed by calculating the Histological Alteration Index (AHI). The AHI data were analyzed by Student's t-test. The values of temperature. O. D., salinity and nitrite obtained were considered within the recommended standards. The pH verified in P6 is considered potentially stressful to fish and, therefore, predisposing to pathologies. The ammonia in P2 is within the standard considered sublethal. In all fish farms evaluated, the presence of total coliforms with high values for the fish farms of São José de Ribamar was verified. The presence of E. colibacteria was verified in P1 indicating fecal contamination of nursery water by the flow of some source of domestic effluent directly into the nursery or the artesian well that supplies the fish culture. Histopathological analyzes performed on the gills indicated morphological alterations in all tissues analyzed. The lesions were: respiratory epithelial lining, lamellar epithelium hyperplasia, blood vessel congestion, lamellar fusion, dilation of the sinus and lamellar aneurysm. The AHI values indicated statistically significant differences between the lesions found in P3 and P4, P3 and P6. Isolation of fungi samples showed the growth of fungi of the genus Penicillium sp., Aspergillus sp. and Fusarium sp. fungi producing mycotoxins. These species are associated with inadequate processing and storage of feed. The occurrence of these fungi may be environmental or may be related to the use of contaminated feed in the farms. The presence of mycotoxins in food has been associated with several fish pathologies. It is worth mentioning that there must be high fungal counts in the diet to indicate the presence ofmycotoxins