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The effects of cypermethrin-based insecticide (CBI), commonly used in aquaculture and agriculture, were evaluated in matrinxa (Brycon amazonicus) exposed to sub-lethal concentration (20% of LC50) for 96 h. Physiological and biochemical effects were studied through biomarkers: lipid peroxidation (LPO), glutathione (GSH), and ascorbic acid concentrations; superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glucose-6-phosphate dehydrogenase (G6PDH) assays in the liver and gills. Besides, ions Na, Cl, and K; protein and glucose concentrations were measured in the plasma. Red blood cells count (RBC), hemoglobin concentration (Hb), hematocrit (Ht), and hematimetric parameters were evaluated in the total blood. The NKA (Na /K+ ATPase) activity was assayed in the gills. The histopathological effects of CBI were also investigated in the gills. The liver and gill LPO increased 62 and 100%, respectively. The tripeptide GSH concentration reduced in the liver and increased in the gill of exposed fish. The SOD and CAT activities increased in the liver, whereas CAT reduced in the gill. Liver also presented an increase in G6PDH activity. Plasma Na and Cl and glucose concentrations increased in the exposed fish. Levels of Ht, Hb and RBC were significantly increased. The gill NKA activity also increased. Exposed fish exhibited histological alterations in the gills such as hypertrophy and proliferation of chloride cells, blood vessels dilation, aneurysms and hemorrhage of the lamella. The histological index indicated moderate to heavy damage to the gills. CBI provokes liver and gills oxidative stress, gill structural damages, and ionic imbalance. A multi-biomarker approach allows us to see that B. amazonicus was unable to cope with CBI exposure.

Pyrethroids are insecticides widely used in agriculture to control ectoparasites and biological vectors. They can reach the water bodies by leaching and or runoff. Fishes are highly sensitive to pyrethroids and the nervous system sensibility and the deficient drug metabolism are the clues but the toxicity mechanisms are yet unclear. The acute toxicity assays allow evaluating the potential, environmental risks of specific pesticides. Type II pyrethroids are becoming widely used and there is no law concerning the limits of use to this kind of pesticide in Brazil. The LC 50 ;96h was evaluated for three pyrethroid basedinsecticides (PBI): cypermethrin, deltamethrin and λ-cyhalothrin in fish Brycon amazonicus. The LC 50 ;96h for the cypermethrin based-insecticide (CBI) was 36 µg L -1 ; for deltamethrin based-insecticide (DBI) was 2.6 µg L -1 ; and for λ-cyhalothrin (LBI) was 6.5 µg L -1 . During the tests some behavioral alterations were registered just after the exposure; they were more evident at the highest xenobiotics concentrations. These alterations were indicative of asphyxia and nervous system damages. The three insecticides are highly toxics to B. amazonicus and the degree of toxicity is: deltamethrin> λ-cyhalothrin> cypermethrin. The behavioral alterations observed are worrying since long-term exposure to sublethal concentrations can affect survival and reproductive ratios.

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