HISTOPATHOLOGICAL EFFECTS OF CADMIUM ON THE GILLS OF THE FRESH-WATER FISH, MACROPSOBRYCON URUGUAYANAE EIGENMANN (PISCES, ATHERINIDAE)

Evaluations of histopathological lesions in gill tissue were carried o ut in the freshwater fish Macropsobrycon uruguayanae following 30 and 60 days of exposure to 1.5 mg l(-1) of cadmium. The study was conducte d on both fed and starved animals in order to determine the influence of feeding condition on cadmium toxicity. The main lesions observed an d quantified were: (1) hyperplasia of primary lamellar epithelium; (2) hyperplasia of secondary lamellar epithelium; (3) separation of respi ratory epithelium; (4) shortening of secondary lamellae; (5) epithelia l necrosis; (6) fusion of adjacent secondary lameliae; (7) hypertrophy of respiratory epithelium; (8) lamellar telangiectasis; (9) hyperplas ia of chloride cells; (10) mucinous metaplasia; and (11) inflammatory infiltration. Lesions 6, 8, 3 and 11 were only induced by exposure to cadmium, while lesion 4 could be produced only by starvation. Starved fish also showed a reduction in total body weight and length. Lesion 2 was shown to be non-specific, and produced by either cadmium, starvat ion or even exposure time. The possible mode of action of the experime ntal factors are discussed in relation to the observed pathologies.