Cadmium‐induced changes in gill morphology of zebrafish, Brachydanio rerio (Hamilton–Buchanan), and rainbow trout, Salmo gairdneri Richardson

Abstract

Freshwater zebrafish and brackish water rainbow trout were exposed to different concentrations of cadmium for up to 6 weeks. The gill morphology was examined by light and electron microscopy, and a morphometric analysis was performed. The morphometric study of the secondary lamellae revealed an increase in the portion exterior to the basal lamina, resulting in an increased diffusion distance, after exposure to cadmium concentrations of 10μg l−1 and above. In both species this was due to an increase in volume of the non‐tissue spaces of the secondary lamellar epithelium. Furthermore, the water space between neighbouring secondary lamellae was clearly reduced. Morphological examination revealed some gross alterations compared with control fish. These initially consisted in curling of the secondary lamellae and finally resulted in local teleangiectasia. Partial lifting of the secondary lamellar epithelium from the pillar cells resulted in large non‐tissue spaces which were invaded by leucocytes. The first sign of degeneration was observed in the chloride cells, which were characterized by a dispersed cytoplasm and a smooth apical plasma membrane.