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Mercury toxicity in tilapia, Oreochromis niloticus, (Linnaeus, 1758)

resumo -O estudo da hematologia é considerado uma importante ferramenta para o processo de diagnóstico de doenças. As técnicas usadas em mamíferos são amplamente aplicadas em peixes, no entanto com algumas modificações. A presença de eritrócitos nucleados e trombócitos em peixes pode causar dificuldade na identificação das cé-lulas sangüíneas, principalmente na contagem de leucócitos totais. A presente pesquisa foi realizada com o objetivo de avaliar duas metodologias (direta e indireta) de quantificação de leucócitos. Espéci-mes de tilápia foram divididos ao acaso em quatro grupos de 48 peixes cada. Cada grupo foi dividido em três réplicas experimentais com 16 animais por réplica em aquários de 40 L e mantidos por 10 dias. A quantificação dos leucócitos foi determinada em 6 animais por grupo nos tempos: 0, 3, 7 e 10 dias. A metodologia direta em câmara de Neubauer apresentou grande oscilação dos dados com relação à média, o oposto tendo sido observado na metodologia indireta realizada em extensões sanguíneas, que apresentou maior homogeneidade entre os grupos. Devido a este fator a metodologia indireta pode ser considerada mais confiável que a metodologia direta para quantificação de leucócitos em peixes.Palavras-chave: Sangue, leucócitos, peixe, Oreochromis niloticus.abstract -Haematological investigation is an important part of disease diagnosis. The techniques used for mammals are generally applicable for fishes with slight modification. The presence of nucleated erythrocytes and thrombocytes in fish may cause some confusion in the identification of blood cells, mainly in total leukocytes count. This work evaluated two different methods (direct and indirect) of leukocytes counting. Specimens of tilapia were divided randomly into four groups of 48 fish each. Each group was further randomized into three replicate experiments of 16 fish per replicate in 40 L aquarium and maintained for 10 days.Counting of leukocytes in peripheral blood was determined in six fishes per group at the times: 0, 3, 7 and 10 days. The direct method in Neubauer chamber showed a large dispersion of data in regard to the average, the opposite was observed in indirect method determined in blood smears that showed more homogeneity among groups. Due to this factor the indirect method can be considered more accurate than the direct method for counting leukocytes in fishes.Key words: Blood, leukocytes, fish, Oreochromis niloticus. introduÇÃoA aqüicultura é um dos sistemas de produção que mais cresce no mundo. Baseado em estatísticas da FAO (1999), a produção brasileira, nos últimos anos tem aumentado na proporção de 30% ao ano. Assim, a aqüicultura começa a desempenhar importante papel econômico e social no cenário nacional, consolidandose como atividade em expansão, gerando alimentos, empregos, impostos e divisas (BORGHETTI e OSTRENSKY, 1998).A tilápia, Oreochromis niloticus, é uma das espécies mais indicadas para o cultivo intensivo principalmente em países tropicais como o Brasil, onde as temperaturas favorecem seu desempenho. Além disso...

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-The objective of this work was to verify the occurrence of compensatory growth in Malaysian prawn (Macrobrachium rosenbergii) reared in pens, after being stocked in cages under high densities during nursery phase. The experiment was carried out in 0.5 m 2 cages and 2-m 2 pens set in natural bottom pond with 2,400 m 2 . Prawn post-larvae (PL) with an average weight of 0.026 ± 0.012 g (nursery phase) were initially stocked in 16 cages at the densities of 50, 400, 800 and 1,200 PL m -2 . Sixty days later, prawns were transferred to 16 growing pens, at the density of 12 prawns m -2 . Initial average weight of the prawn in this phase was the final average weight registered in the nursery phase, as follows:

Fish bioassays are valuable tools that can be used to elucidate the toxicological potential of numerous substances that are present in the aquatic environment. In this study, we assessed the antagonistic action of selenium (Se) against the toxicity of mercury (Hg) in fish (Oreochromis niloticus). Six experimental groups with six fish each were defined as follows: (1) control, (2) mercury (HgCl(2)), (3) sodium selenite (Na(2)Se(4)O(3)), (4) sodium selenate (Na(2)Se(6)O(4)), (5) mercury + sodium selenite (HgCl(2) + Na(2)Se(4)O(3)), and (6) mercury + sodium selenate (HgCl(2) + Na(2)Se(6)O(4)). Hematological parameters [red blood cells (RBC), white blood cells (WBC), and erythroblasts (ERB)] in combination with cytogenotoxicity biomarkers [nuclear abnormalities (NAs) and micronuclei (MN)] were examined after three, seven, ten, and fourteen days. After 7 days of exposure, cytogenotoxic effects and increased erythroblasts caused by mercury, leukocytosis triggered by mercury + sodium selenite, leukopenia associated with sodium selenate, and anemia triggered by mercury + sodium selenate were observed. Positive correlations that were independent of time were observed between WBC and RBC, ERB and MN, and NA and MN. The results suggest that short-term exposure to chemical contaminants elicited changes in blood parameters and produced cytogenotoxic effects. Moreover, NAs are the primary manifestations of MN formation and should be included in a class characterized as NA only. Lastly, the staining techniques used can be applied to both hematological characterization and the measurement of cytogenotoxicity biomarkers.

INTRODUCTION: Frog farming, if not well managed, may cause environmental damages. The use of antibiotics, the organic discharge and the introduction of exotic species can disseminate risks such as eutrophication, changes in the water quality and organic pollution, factors that affect the human consumption. AIM: Evaluating the water quality of a bullfrog farming system, discussing their relations to production and the environment based on the current legislation. METHODS: Sampling was performed on a monthly basis from November 2006 to March 2007 during growth and fattening phases of bullfrog (Lithobates catesbeianus). Sample sites were distributed according to the water flow: upstream from the mixing zone, affluent (supply water), bay, effluent, mixing zone and downstream from the mixing zone. In the field, pH, electrical conductivity, dissolved oxygen, temperature and turbidity were measured. In laboratory, nitrogen, phosphorus and chlorophyll a concentrations were analyzed. RESULTS: The concentration of nutrients was determiner for water quality in the bay and its effluent. According to the current legislation, the effluent exceeded the limits for total phosphorus (> 0.030 mg L-1) and total nitrogen (> 1.27 mg L-1). Other variables presented acceptable values in light of the current laws. CONCLUSION: The high values of nutrients and other factors such as conductivity and turbidity are proportional to the animal growth due to the inadequate management practices evidenced by feed conversion rate. The following management options are proposed: maintaining the flow and decreased density of animals; maintaining the flow and density storage with adequate control of the food supply.