Bath exposure of Atlantic halibut (Hippoglossus hippoglossus L.) yolk sac larvae to bacterial lipopolysaccharide (LPS): Absorption and distribution of the LPS and effect on fish survival

Radiolabelled bacterial lipopolysaccharide (H-3-LPS) obtained from Aeromona s salmonicida subsp. salmonicida was added to the petri dishes containing y olk sac larvae of Atlantic halibut (Hippoglossus hippoglossus L.). The larv ae were exposed either to 6.25, 12.5, 25, 50 or 100 mu g H-3-LPS ml(-1). Th e uptake was both dependent on the LPS concentration and the time of exposu re. After 5 days of exposure, each larva contained 1.8-7.4 ng H-3-LPS depen dent on the initial concentration. After 10 days of exposure each larva con tained 7.0-12.4 ng LPS and after 15 days they contained 18.3-34.9 ng 3H-LPS . Fluorescence microscopic analysis of sections obtained from larvae expose d to FITC-LPS (25, 50 and 100 mu g ml(-1)) for 5, 10 and 15 days, revealed fluorescence in intestinal epithelial cells, cells in the connective tissue adjacent to the intestine, in cells located between the integumental layer and yolk sac, and in some epithelial cells in the integument. By use of im munohistochemical techniques, LPS was confined to intestinal epithelial cel ls, lumen of excretory duct and in numerous cells in the epidermal layer. C ontrol specimens did not contain fluorescence or were immunohistochemically negative for LPS. In groups of larvae exposed to 12.5, 25, 50 and 100 mu g LPS ml(-1), the survival was significantly increased after exposure to 50 and 100 mu g LPS ml(-1) from day 20 (96 d degrees) and throughout the yolk sac period compared to untreated larvae. (C) 2000 Academic Press.