Histopatological analysis of the liver of Nile tilapia, Oreochromis niloticus, reared in cage in Guarapiranga Reservoir, São Paulo State, Brazil

Abstract

Aiming to know if the ambient conditions of the Guarapiranga Reservoir (São Paulo State) were adjusted for the development of the aquatic organisms that live there, it was proposed the evaluation of the histopathologic alterations of the liver of fingerlings of Nile tilapia, Oreochromis niloticus (Linnaeus, 1757) reared in cages installed in that Reservoir. Monthly, in a period of eight months (Sep./1997-Mar./1998), 5 specimens of one of the cages were captured and sacrificed by cerebral commotion in order to register the total length and weight, so as to collect samples of the liver, that were fixed in 10% formalin, included in paraffin and stained by Hematoxylin-Eosin and by the Schiff Periodic Acid method (PAS) for glycogen detection. After the eight months of observations, a total of 40 specimens had been analyzed, having the total length ranged from 8.7 to 19.7 cm, and the weight, from 12.0 to 135.0 grams. The anatomopathologic analysis of the liver of O. niloticus allowed to observe that in the majority of the specimens, the liver presented alterations in different degrees, consisting of a deformed and extremely friable mass with a bad smell. Histopatologically, it was observed the hepatic parenchyma with polygonal hepatocytes arranged in laces, with indefinite forms, sometimes with vacuolization. The hepatocytes nucleus presented variation in the diameter and chromatin condensation with or without nucleoli. The presence of picnotic nuclei was also noticed progressing to cariolysis, and vacuolated cytoplasm with dense granulations was present. In some fish, it was observed low degree of hepatic glycogen in relation to that registered in the liver of other specimens. Ahead of these comments, it was possible to presume that the alterations observed in the liver were probably related to the action of toxic or xenobiotic substance present in the water of Guarapiranga Reservoir.