Impact of bacterial infection on activity, buoyancy, and mortality of halibut and turbot yolk-sac larvae

Eggs of halibut (Hippoglossus hippoglossus L.) and turbot (Scophthalmus maximus L.) were exposed to Flexibacter ovolyticus and pathogenic Vibrio sp. strains prior to, and during, hatching. Activity, buoyancy, and mortality of the yolk-sac larvae were monitored from hatching to day 34 for halibut and to day 6 for turbot. Both the Flexibacter-infected and the Vibrio-infected halibut larvae had a significantly lower activity than larvae in the control group. The infected larvae also had a higher specific density. Vibro-infected turbot larvae had a lower activity than Flexibacter-infected larvae and the uininfected larvae. Mortality in the Flexibacter-infected halibut larvae and Vibrio-infected turbot larvae was higher than in the control groups. The mortality in the Vibrio-infected halibut larvae showed a dose-response to bacterial count.