Hematological and physiological changes in the blood of juveniles of the freshwater fish, Prochilodus scrofa were determined after acute exposure to 20, 25, and 29 µgCu L -1 in water (pH 7.5; hardness 24.5 mg L -1 as CaCO 3 ) for 96 h. Copper exposure to 25 and 29 µgCu L -1 caused significant increase in the hematocrit and red blood cell values. The increase in red blood cells was associated with increase in whole blood hemoglobin only in fish exposed to 29 µgCu L -1 . Leukocytes increased following copper exposure and were significantly higher in fish exposed to 29 µgCu L -1 . Differential leukocyte percentage displayed significant reduction in lymphocytes and an increase in neutrophils in fish exposed to 25 and 29 µgCu L -1 . The percentage of monocytes remained unchanged after copper exposure. The thrombocytes did not change. There was a significant decrease in plasma [Na + ] and [Cl -] and a significant drop in blood pH in fish exposed to 25 and 29 µgCu L -1 while [K + ] showed significant increase in fish exposed to 29 µgCu L -1 . Copper exposure led to ionoregulatory impairment, although chloride cell hypertrophy was induced. The changes in red blood cells suggest a compensatory response to respiratory surface reduction of gills (tissue damage and cell proliferation) in order to maintain oxygen transference from water to the tissues, allowing the fish to survive during the so-called shock phase of LC 50 exposure, at least while at rest. tenha sido induzida, e as mudanças nos parâmetros hematológicos sugerem resposta compensatória à redução da superfície respiratória das brânquias (lesões no tecido branquial e proliferação celular) de forma a manter a transferência do oxigênio da água para o sangue, permitindo a sobrevivência dos peixes durante a fase de choque da exposição a CL 50 , pelo menos, sob condições de repouso.Palavras-chave: cobre, parâmetros hematológicos, íons plasmáticos, histopatologia branquial, Prochilodus scrofa.

Prochilodus lineatus Valenciennes (curimbatá)is an important migratory Neotropical fish. It does not feed during spawning migration, and often survives after spawning. The mobilization of energy reserves and some effects of starvation (zero to eight weeks) on fish health were experimentally evaluated. Hepatic glycogen and lipids from the perivisceral fat bodies were the main reserves mobilized during the first four weeks of fasting. During this period, somatic indices and blood parameters showed that fish health was not significantly affected. However, after five weeks of food deprivation, the main energy reserves were depleted and the fish became anaemic. The loss of muscle mass indicates that protein breakdown was an important energy source after the reduction of hepatic and perivisceral reserves. Mortality was increasingly observed from seven weeks of starvation. Prior accumulation of high amounts of reserves is essential to allow movements for long distances during spawning migrations in this species.

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