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

Development of skin lectin and the lymphoid tissues were studied in the lep tocephalus larvae of the Japanese eel Anguilla japonica. The specimens rang ing in total length from 11 to 58 mm were captured at 12-19 degrees N, 131- 137 degrees E and at 21-23 degrees N, 123-128 degrees E in the Pacific Ocea n. The skin of leptocephali contained extremely active lectin which aggluti nated rabbit red blood cells the same as adults. Club cells, known as lecti n secreting cells, were also recognized in the epidermis of leptocephali, a lthough the shape was not an elongated club form but oval. The cells were c onfirmed to contain lectin in the secretory vacuole by an immunofluorescenc e technique. The lectin in the cells was also recognized in the 8 days post -hatch preleptocephalous larvae, which was obtained from an artificially sp awned eel, suggesting the importance of the lectin in the early larval deve lopment. In contrast, lymphoid tissues concerning immune functions showed d elayed development with the exception of the thymus. No blood cells were se en in the kidney and spleen, even in a large specimen. Only a few undiffere ntiated leukocyte-like cells could be observed, some of them showed phagocy tic figures. The thymus along with many thymocytes could be seen in the sma llest leptocephalus of total length (TL) 11 mm. T cells may have a function in defense mechanisms during the leptocephalus stage, although other immun e cells were still underdeveloped.