No abstract

Gills are vital structures for fish, since they are the main site for gaseous exchange as well as partially responsible for osmorregulation, acid-basic balance, excretion of nitrogenous compounds and taste. Chemicals in the water may alter the morphology of branchial cells of fish that are, therefore, a useful model for environmental impact and ecotoxicology studies. In order to investigate the effects of an organophosphorous compound, methyl parathion, on the gills of the fish, samples of Metynnis roosevelti were exposed to lethal (7ppm) and sublethal (1ppm) doses of Mentox 600 CE. Through light and scanning electron microscopy, shrinking of the branchial epithelium, followed by detachment and hyperplasia were observed. Externally, the branchial filaments presented the gradual disappearance of microridges. Even in sublethal doses, the organophosphorous reduced the health and fitness of these fish, as consequence of secondary effects derived from changes in the branchial epithelium, impairing oxygenation and ionic balance of the organism.
As brânquias são estruturas vitais para peixes, pois são o principal local de trocas gasosas, assim como parcialmente responsáveis pela osmorregulação, pelo equilíbrio ácido-básico, pela excreção de compostos nitrogenados e pela gustação. Compostos químicos na água podem alterar a morfologia das células branquiais de peixes, que se constituem, dessa forma, em um útil modelo para estudos de impacto ambiental. Visando investigar os efeitos de um composto organofosforado, o metil paration, em brânquias de peixes, exemplares de Metynnis roosevelti foram expostos a doses letais (7ppm) e subletais (1ppm) de Mentox 600 CE. Observações em microscopia óptica e eletrônica de varredura evidenciaram enrugamento do epitélio branquial, seguido por descolamento e hiperplasia. Externamente, os filamentos branquiais apresentaram desaparecimento gradual das microssaliências. Os resultados mostram que, mesmo em doses subletais, o organofosforado poderá levar o animal a sofrer conseqüências secundárias decorrentes das alterações da superfície de trocas gasosas e iônicas

ABSTRACT. Among the new substances that were synthesised by the chem ical industlY during the last decades, with the aim to improve human prosperity, some cause negative effects on non target organisms like fish. Among the pesticides, the organophosphates (OP) are w idely used in cattle management, agriculture and aquaculture activi ties. Brachydania reria Hamilton-Buchman, 1822 is used world-wide in fishtests for the establishment of the lethal levels of pesticides. Nevertheless, these fi sh show mo rphological changes in their hepatocytes when exposed experimentally for 24 hours to the sublethal dose of 0.025 fli /l of the OP Dimethoate 500, in ac ute tests.Eight hours after exposure, a high density ofeells with cytoplasmic granulation is seen as well as focal necrosis. The main changes that occurred in the first 24 hours of exposure we re the loss of the typical polygonal ce ll shape and of detec tab le cell limits, lateral migration of nuclei, nuclear size and shape, condensati on of chromatin and pycnosis, increased cytoplasm ic granulation followed by vacuo li sati on. After 48 hours in clean water, 72 hours ti'om contaminati on, besides significant morpho logica l changes and necrosis, focal regeneration of the hepatocytes, canaliculi , ducts and sinusoids were seen. Even having been exposed to the half of the dose considered as safe according to the general pesticide allowance rules, significant changes of the liver ti ssue were obselved.

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The digestive system of Trichomycterus brasiliensis (Lütken, 1874), a small sized tropical Teleostean fish widely distributed in South America, was studied. Tissue samples were prepared for light and scanning electron microscopy (SEM). Trichomycterus brasiliensis shows stratified esophagus epithelium with taste buds and goblet cells with neutral and acid mucus at the anterior region. The stomach is caecal, presenting a pyloric valve with neutral mucus cells. At the terminal portion it is surrounded by a thick muscular wall. The intestine shows two loops; the epithelium is single columnar, with acid and neutral mucus in goblet cells. Multicellular intestinal glands are absent. Granular cells are often seen in the mucosa, less in the submucosa but were not observed in the muscularis. After the intestine-rectal valve, the rectum shows lower mucosal folds, more goblet cells and a thicker muscularis. No lobes were observed at the liver. Small regions of pancreatic tissue may be identified within the hepatic tissue mainly surrounding vessels and ducts. A compact pancreas may also be observed ventrally to the stomach and covering the bile duct. The possible significance of the heterogeneous character of the digestive tube mucosubstances is discussed. The digestive system of T. brasiliensis presents structural characteristics of a predator fish