Selection of bacteria and the effects of bacterial treatment of Atlantic halibut (Hippoglossus hippoglossus L.) eggs and larvae

Bacteria dominating the cultivable gut community of overall successful first feeding halibut (Hippoglossus hippoglossus L.) larvae were tested for their in vitro growth inhibition activity against selected fish pathogenic bacteria and isolates dominating the cultivable gut community of larvae with an overall poor success. A mixture containing equal numbers of three isolates was selected for the treatment of halibut eggs through repeated bathing, and larvae through grazing of live prey in a mixture of the selected isolates prior to offering to larvae. The isolates were found as a part of the dominating bacterial community of treated eggs and treatment was not found to affect egg survival. Improved larval survival was observed as a result of offering bacteria-treated live prey to larvae, and improved larval growth was observed in one of the two experiments that were carried out in commercial size production units. The bacterial community structure of the live prey, analysed using PCR and denaturing gradient gel electrophoresis, was only partly reflected in larvae after one week in feeding. A successful colonization of fertilized eggs by the isolates used for treatment entails the possibility to establish a favourable bacterial environment already prior to hatching.