Abstract
To elucidate the process of the uptake of suspended particles into the skin, fins and gills of rainbow troutOncorhynchus mykiss, 100 fingerlings were immersed in a suspension of 1μm diameter fluorescent microspheres and rinsed with water. The fate of microspheres adhering to body surface was traced for elapsed times ranging from 1 min to 24 h. Although most microspheres were removed in a 2 h-rinse with water, a few were observed by light microscopy to be located in both epidermal and dermal tissues which had microscopic injuries. As observed by electron microscopy, microspheres were taken up by migrating epithelial cells, or embedded in the dermis covered with these cells. Some of those microspheres embedded in dermis were endocytosed by macrophages. Such features were confirmed in artificial wound experiments. We conclude that microscopic injuries to trout could be an important route for the uptake of antigen administered by immersion, 2 to 24 h after fish suffer from injuries.
