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 (3H-LPS) obtained from Aeromonas salmonicida subsp. salmonicida was added to the petri dishes containing yolk sac larvae of Atlantic halibut (Hippoglossus hippoglossus L.). The larvae were exposed either to 6·25, 12·5, 25, 50 or 100 μg3H-LPS ml−1. The uptake was both dependent on the LPS concentration and the time of exposure. After 5 days of exposure, each larva contained 1·8–7·4 ng3H-LPS dependent on the initial concentration. After 10 days of exposure each larva contained 7·0–12·4 ng LPS and after 15 days they contained 18·3–34·9 ng3H-LPS. Fluorescence microscopic analysis of sections obtained from larvae exposed to FITC-LPS (25, 50 and 100 μg 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 immunohistochemical techniques, LPS was confined to intestinal epithelial cells, lumen of excretory duct and in numerous cells in the epidermal layer. Control specimens did not contain fluorescence or were immunohistochemically negative for LPS. In groups of larvae exposed to 12·5, 25, 50 and 100 μg LPS ml−1, the survival was significantly increased after exposure to 50 and 100 μg LPS ml−1from day 20 (96 d°) and throughout the yolk sac period compared to untreated larvae.