Intact antigen uptake in intestinal epithelial cells of marine fish larvae

Endocytosis of bacteria by epithelial cells in the hindgut of 4- to 6-day-old cod ( Gadus morhua L. ) larvae and of 10- to 12-day-old herring ( Clupea harengus L. ) larvae was demonstrated by fluorescence microscopy and transmission electron microscopy. Fixed sheep erythrocytes and bacteria-sized latex particles were not ingested by these cells. By immunohistochemical methods intact bacterial antigens were observed in columnar epithelial cells in the foregut of 4-day-old yolk-sac larvae of cod. In these cells a preferential uptake of Vibrio fischeri and Vibrio salmonicida cells as compared to Flavobacterium sp. was found. The possible role of these findings in the establishment of an indigenous microflora, defence against pathogens or nutrient absorption in fish larvae is discussed.