QUANTITATIVE-ANALYSIS OF ALTERATIONS IN LIVER ULTRASTRUCTURE OF RAINBOW-TROUT ONCORHYNCHUS-MYKISS AFTER ADMINISTRATION OF THE AQUACULTURE ANTIBACTERIALS OXOLINIC ACID AND FLUMEQUINE

The 4-quinolone antibacterials oxolinic acid and flumequine are routin ely and successfully used in commercial aquaculture. In order to inves tigate the effects of these antibiotics on fish Liver ultrastructure, rainbow trout were fed diets containing oxolinic acid or flumequine at concentrations of 1.0 and 1.2 g kg(-1) food, respectively, at a ratio n of 1% body weight d(-1) for 10 d. Fish were sampled for examination on Days 1 and 10 after a return to normal diet and hepatic ultrastruct ural alterations were quantified by stereological analysis. Both drugs induced an almost 2.5-fold increase in the volume of the rough endopl asmic reticulum, which displayed phenomena of dilation, vesiculation a nd fragmentation. Glycogen deposits were depleted to approximately 50 % of their control volume accompanied by the formation of clusters of lipid droplets. Additional structural alterations included the intraly sosomal accumulation of stacked membranes and the presence of elaborat ed myelin figures interspersed in the cytoplasm. No drug-specific resp onses were observed. In general, compensatory rather than degenerative changes followed the antibiotic administration. Further signs support ing a stimulation in the hepatocellular metabolic activity were mitoch ondrial hyperplasia after flumequine administration and high nuclear-c ytoplasmic ratios in individuals treated with oxolinic acid.