Experimental infection of turbot Scophthalmus maximus and halibut Hippoglossus hippoglossus yolk sac larvae with Aeromonas salmonicida subsp salmonicida

The susceptibility of early life stages of turbot Scophthalmus maximus and halibut Hippoglossus hippoglossus to Aeromonas salmonicida subsp. salmonicida was studied in challenge experiments. Eggs of both fish species (and the larvae hatching from the eggs) were exposed to the bacterium. Larvae of both species experienced mortality during the yolk sac stage, apparently as a result of the challenge. Examination of histological sections revealed degenerative changes in the skeletal muscle of both species of larvae. The bacterium could not be recovered from the larvae by culture, but it was shown to be present in the intestinal lumen of some of the turbot larvae examined using an immunohistochemical technique known to be specific for the bacterium. The results indicate that marine fish larvae exposed to A. salmonicida subsp. salmonicida may become infected and that the bacterium may persist in the larvae. Turbot larvae seemed to be more susceptible than halibut larvae.