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With the objective of evaluating the effects of organochlorine pesticides (aldrin and heptachlor) on the survival, growth and gill morphology of juvenile zebrafish (Danio rerio), four partial chronic toxicity bioassays were conducted (seven days' duration) with both compounds in a semi-static system with renewal every 24 h. The results did not show any effects on the fish's survival, but did on their growth and gill morphology. Aldrin was more toxic than heptachlor, since the chronic value (CV) for growth was nearly 8.7 times less, a result confirmed by analyzing the histology of the gills, in which the changes detected were considered more severe for the former substance. In general, they were found branchial lesions of first stage, in other words, cell proliferation between the secondary lamellae, hyperplasia, lifting of respiratory epithelial cells; fusion of several secondary lamellae and dilation of blood vessels. Aneurysms (alterations of second stage) they were verified in the exposed organisms to the aldrin, which also presented about 10% of reduction in the standard length and 30% of reduction in the total weight in relation to the exposed organisms to the control. For heptachlor these values were of 8% and 25%, respectively. The intensity of the gill lesions and growth of the fish did not depend on the pesticide concentration, suggesting different modes of action of the products.

Toxicity tests using early life stages of fish are of great importance in assessing risks to growth, reproduction and survival in polluted environments and are important tools for good environmental monitoring. However, a small number of standard bioassays of this type have been developed in Brazil. Curimbatá (Prochilodus lineatus) is an abundant South American characid fish of great commercial interest. It was chosen for testing different concentrations of 40% dimethoate, an organophosphate insecticide and acetylcholinesterase enzyme (AChE) inhibitor used widely in Brazil. The 48-h LC 50 for eggs is higher than 16.0 µg.L -1 , whereas for recently hatched larvae it was found to be significantly lower (11.81 µg.L ) and also significantl y lower than that for eggs by a Student t-test for independent samples (p = 0.03). The 96-h LC 50 for 3-day old larvae was 10.44 µg.L -1 (8.03 µg.L -1 -13.57 µg.L -1 ), similar to that of recently-hatched larvae (p = 0.76). Larval mobility was also found to be reduced by this insecticide.Keywords: pesticide, toxicity, fishes, bioassay, larvae. resumo toxicidade do acaricida organofosforado dimetoato 40% aos ovos e larvas deProchilodus lineatus (Prochilodontidae, characiformes)Os testes de toxicidade com os primeiros estágios de vida de peixes são de elevada importância no que se refere ao comprometimento das fases de crescimento, reprodução e sobrevivência dos organismos em ambientes poluídos, constituindo uma ferramenta importante para um adequado monitoramento ambiental. Entretanto, um pequeno número de bioensaios desta natureza tem sido desenvolvido no Brasil. O curimbatá (Prochilodus linetaus) é um peixe da ordem Characidae de grande interesse comercial e muito abundante na América do Sul. A espécie foi utilizada para testar diferentes concentrações de dimetoato 40%, um pesticida organofosforado inibidor da enzima acetilcolinesterase (AChE) utilizado em grande escala no Brasil. A CL50 (48h) para ovos é superior a 16,0 µg.L -1; entretanto para larvas recém-eclodidas foi significativamente mais baixa (11,81 µg.L -1 , variando de 10.23 a 13,65) de acordo com o teste-t para amostras independentes (p = 0.03). A CL50 para larvas com 3 dias de vida foi de 10,44 µg.L -1 (8,03-13,57), apresentando-se similar ao resultado encontrado para larvas recém-eclodidas (p = 0.76). A mobilidade das larvas foi reduzida na presença deste pesticida. toxicidade, peixes, bioensaios, larva. 634 CAMPAGNA, A. F. et al. Palavras

AIM: Artificial sediments with simple formulations were used to assess the toxicity of Cr to C. xanthus, D. rerio and P. reticulata. METHODS: The organisms were exposed to two sediment formulations: one without organic matter (S0) and one with 1% organic matter (SIII), both contaminated with Cr at concentrations of 90, 180, 360, 720 and 1440 mg/kg for the assays with C. xanthus, and 375, 750, 1500 and 3000 mg/kg for those with the two fish species. Chromium was obtained from the potassium dichromate (K2Cr2O7). RESULTS: The results of the acute toxicity tests demonstrated a reduction of up to four times in toxicity with the presence of OM, consisting of biodegradable detritus, even at the low concentration used (1%), and that C. xanthus was most sensitive to the metal. The reduction in the chromium toxicity was indicated by the LC50 values, which were higher in SIII (1234.43 mg/kg; 2263.54 m/kg; 2244.48 mg/kg) than in S0 (340.56 mg/kg; 1731.04 mg/kg; 1733.55 mg/kg) for C. xanthus, D. rerio and P. reticulata, respectively. CONCLUSIONS: Because of the repeatability of the results obtained, the artificial sediments with simple formulations were satisfactory to assess toxicity and can thus provide reliable results in ecotoxicological studies