A 45 day experiment was carried out to evaluate the effect of water salinity on the performance, haematological parameters and histological characteristics of the gills of the Nile tilapia, Oreochromis niloticus. The water salinity levels evaluated were: 0, 7, 14 and 21 g L-1. Nile tilapia specimens (1.62 ± 0.01 g), distributed into 20 fibreglass tanks (100 L) at a density of 15 fish per tank. There were no significant differences of the water salinity levels on daily feed intake; however, there were differences (P < 0.05) on the daily weight gain, feeding conversion rate and survival. The best results were observed for the water salinity levels of 0 and 7 g L-1. There were no differences (P > 0.05) between these levels. Regarding the haematological parameters, it was observed that the percentage of the haematocrits and the erythrocyte count were influenced (P < 0.05) by the water salinity level, which was not observed for the leukocyte count. The observed histopathological alterations were chloride cell hypertrophy, epithelial lifting, structure alteration, telangiectasia, primary lamellae cells aggregation, fusion and occurrence of aneurisms of different sizes in some secondary lamellae. Regarding the frequency of gills infection intensity, there were slight changes between the salinities of 0, 7 and 14 g L-1 and moderate changes at 21 g L-1. It is concluded that Nile tilapia can be reared in water salinities of up to 7 g L-1 without damage to the parameters evaluated in this work.

Se realizó un experimento de 45 días para evaluar el efecto de la salinidad sobre el crecimiento, parámetros hematológicos y características histológicas de las branquias de la tilapia del Nilo, Oreochromis niloticus. Los niveles de salinidad fueron: 0, 7, 14 y 21 g L-1. Los especímenes de tilapia del Nilo (1,62 ± 0,01 g) se distribuyeron en 20 estanques de fibra de vidrio (100 L) a una densidad de 15 peces por estanque. No hubo diferencias significativas en los niveles de salinidad sobre el consumo diario de alimento, pero hubo diferencias (P < 0,05) en la ganancia diaria de peso, conversión alimenticia y supervivencia. Los mejores resultados se observaron en los niveles de salinidad de 0 y 7 g L-1, sin diferencias (P > 0,05) entre ellos. En cuanto a los parámetros hematológicos, se observó que el porcentaje de hematocrito y número de eritrocitos fueron influenciados (P < 0,05) por el nivel de salinidad, que no se observó para el recuento de leucocitos. Las alteraciones histopatológicas observadas fueron: hipertrofia de las células de cloruro, elevación epitelial, cambio en la estructura, telangiectasia, agregación de las células primarias de las laminillas, fusión y aparición de algunos aneurismas de diferentes tamaños en laminillas secundarias. En cuanto a la frecuencia de la intensidad en la infección de las branquias, hubo ligeros cambios entre las salinidades de 0,7 y 14 g L-1 y cambios moderados a 21 g L-1. Se concluye que la tilapia del Nilo se puede cultivar en salinidades de hasta 7 g L-1 sin daño a los parámetros evaluados en este trabajo.

Pathological alterations and autoecology of Didymocylindrus simplex in Katsuwonus pelamis (Linnaeus, 1758) in the Southwestern Atlantic Ocean off of South America are presented. This is the first record of the species in the region; the specimens are described. The pathologic changes observed most often were infiltration of lymphocytes and slight fibrosis of the connective tissue surrounding the parasite. The typical aggregated distribution pattern was observed for Didymocylindrus simplex Ishii, 1935. Statistical analysis demonstrated no correlation between the abundance and prevalence of parasites with the total length of the host. The sex of the host does not influence the prevalence and intensity of infection.

Este trabalho utiliza índices ecológicos em taxocenoses de peixes (constância de ocorrência, diversidade de espécies, riqueza, equitabilidade, índice de qualidade integrado (IQ)) como instrumento de avaliação da degradação ambiental. As amostragens foram padronizadas e realizadas sazonalmente durante dois anos, com rede de arrasto do tipo picaré, em onze pontos da bacia hidrográfica do lago Guaíba. Os pontos que apresentaram maior regularidade sazonal nos índices coincidem com locais de melhor qualidade ambiental indicados por outros fatores (frequência de anomalias, DBO5, temperatura, coliformes totais, oxigênio dissolvido). O cálculo do índice de qualidade integrado (IQ), entretanto, foi extremamente influenciado pela abundância e riqueza de espécies, sendo que os locais considerados de melhor qualidade por este índice correspondem aos de pior qualidade ambiental indicados por outros fatores. A análise realizada demonstrou que à medida que a qualidade da água melhora, o Índice de Margalef diminui. Isto demonstra que mesmo havendo uma melhora na qualidade da água, não houve uma melhora da estrutura da comunidade deste local.

Several ecological indexes in taxocenoses of fish (constancy, diversity, richness, evenness, and integrated quality index - IQ) are used as indicators of environmental degradation through the analysis of standardized and seasonal fish samples taken along two years in eleven localities of the Lake Guaíba drainage. Localities that showed regular diversity indexes along two years are coincident with those with better environmental quality indicated by other factors (frequency of abnormalities in fishes, DBO5, temperature, total coliforms, dissolved oxygen). The integrated quality index, however, was mostly influenced by abundance and richness, being the localities indicated as the best quality by this index coincident with those indicated as bad quality by other factors. The accomplished analysis demonstrated that when the measure of water quality gets better, the Margalef Index decreases. This demonstrates that even having an improvement in water quality, there is no improvement of structure of the fish community of this place.

Little information is available about natural populations of fishes exposed to polluted waters in Brazil. Contaminants may be lethal or predispose fishes to sickness, being the analysis of aquatic organisms a good indicator of environmental quality. The violinha, Rineloricaria strigilata (Hensel, 1868), is a common loricariid catfish in the Guaíba lake basin, Rio Grande do Sul, Brazil, and has been selected as a bioindicator for being resident, occurring in more than 50% of the samples, and by showing externally detectable neoplasies. These are characterized by its dark pigmentation, bony plates hypertrophy, and hypertrophy and irregular arrangement of the odontodes. Histology showed hypertrophied epitelial tissues, with an increased number of secretory cells, blood cells, and melanina pigments, giving the dark appearance to the neoplasm. Observed frequencies of neoplasm were higher in lake Guaíba than in comparativo samples. Inside lake Guaíba, a pattern of distribution of neoplasm was observed, with the absence of neoplasm in fishes at the collected site that receives water from rio Jacuí, and frequencies of 3.04 to 16.81% in the collection localities in front of Porto Alegre and downstream localities, that receive water from rio Jacuí, rio dos Sinos and rio Gravataí, that drain urban and industrial area of Porto Alegre and neighborhood cities.