Skin lectin and the lymphoid tissues in the leptocephalus larvae of the Japanese eel Anguilla japonica

Abstract

Development of skin lectin and the lymphoid tissues were studied in the leptocephalus larvae of the Japanese eel Anguilla japonica. The specimens ranging in total length from 11 to 58 mm were captured at 12-19°N, 131-137°E and at 21-23°N, 123-128°E in the Pacific Ocean. The skin of leptocephali contained extremely active lectin which agglutinated rabbit red blood cells the same as adults. Club cells, known as lectin secreting cells, were also recognized in the epidermis of leptocephali, although the shape was not an elongated club form but oval. The cells were confirmed to contain lectin in the secretory vacuole by an immunofluorescence technique. The lectin in the cells was also recognized in the 8 days post-hatch preleptocephalous larvae, which was obtained from an artificially spawned eel, suggesting the importance of the lectin in the early larval development. In contrast, lymphoid tissues concerning immune functions showed delayed development with the exception of the thymus. No blood cells were seen in the kidney and spleen, even in a large specimen. Only a few undifferentiated leukocyte-like cells could be observed; some of them showed phagocytic figures. The thymus along with many thymocytes could be seen in the smallest leptocephalus of total length (TL) 11 mm. T cells may have a function in defense mechanisms during the leptocephalus stage, although other immune cells were still underdeveloped.