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Made available in DSpace on 2022-04-29T07:25:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-01-01 Environmental changes affect fish homeostasis, turning them more susceptible to diseases. In Brazil, outbreaks of Streptococcus agalactiae infection have been reported in Nile tilapia when they are outside of their thermal comfort zone. This investigation evaluated mortality rate and which were the most infected organs at temperatures that naturally occurred in southern of Brazil. Forty Nile tilapia (Oreochromis niloticus) were infected with S. agalactiae and distributed in four groups (n=10) and each group was exposed to a different temperature: G1: 24°C, G2: 26°C, G3: 28°C, and G4: 32°C. Fish were monitored for 10 days. In this period, fish that presented irreversible clinical signs were sacrificed and samples of brain, liver, and kidney were collected for bacteriological and molecular analysis. Signs compatible with a streptococcal infection were observed in all groups. Highest mortality rates occurred at 24°C and 32°C. The brain was the most affected organ with the highest percentage of isolation of S. agalactiae by both methods of diagnosis. The results suggest that, as in mammals, temperatures that are further away from the comfort zone influence fish homeostasis, increasing susceptibility to bacterial infections. Universidade Estadual Paulista “Júlio de Mesquita Filho”, Departamento de Patologia Animal Universidade Estadual Paulista “Júlio de Mesquita Filho”, Centro de Aquicultura Universidade do Norte do Paraná, Campus Luiz Meneghel Universidade Estadual Paulista “Júlio de Mesquita Filho”, Departamento de Patologia Animal Universidade Estadual Paulista “Júlio de Mesquita Filho”, Centro de Aquicultura

Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-27T11:26:26Z No. of bitstreams: 0Bitstream added on 2014-05-27T14:47:39Z : No. of bitstreams: 1 2-s2.0-84859208367.pdf: 746043 bytes, checksum: a1cdc1bbab6e541b4d50f6a05739f20e (MD5) Made available in DSpace on 2014-05-27T11:26:26Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-04-04 The present study evaluated the microbiological water quality and tissue lesions in gills from Nile tilapia (Oreochromis niloticus) and hybrid tambacu (Colossoma macropomum female x Piaractus mesopotamicus male). For this, water and gills were collected from fish farming at six locations in Itapecuru- Mirim County, Maranhão State. Microbiological water analyses revealed contamination by total coliforms, Escherichia coli and heterotrophic bacteria. In the gills, we observed a diversity of Gram-positive and Gramnegative bacteria. The tissue lesions were: lamellar fusion, interlamellar hyperplasia, sub-epithelial edema and telangiectasia. Inflammatory lesions were not observed. Significant statistical difference (p > 0.05) was not detected when comparing different gills lesions during rainy and dry season. The correlation between lesion and pond type was statistically different (p < 0.05) for lamellar fusion and interlamellar hyperplasia which occurred more frequently at ground ponds. Regarding the frequency of lesions in the different fish species, there was statistical difference (p < 0.05), and the tambacu was more sensitive to lamellar fusion while tilapia was more sensitive for the other lesions. In relation to the sampling stations, there was statistical difference for all the gill lesions. In conclusion, tissue lesions are nonspecific and function as a defense mechanism against polluted aquatic environments, without infectious character. Departamento de Química e Biologia Universidade Estadual do Maranhão, Cidade Universitária Paulo VI, s/n, São Luís, Maranhão Departamento de Patologia Veterinária Universidade Estadual do Maranhão, São Luís, Maranhão Departamento de Patologia Veterinária Faculdade de Ciências Agrárias e Veterinárias Universidade Estadual Paulista Júlio de Mesquita Filho, Jaboticabal, São Paulo Departamento de Patologia Veterinária Faculdade de Ciências Agrárias e Veterinárias Universidade Estadual Paulista Júlio de Mesquita Filho, Jaboticabal, São Paulo