CHANGES IN BEHAVIOR OF ATLANTIC HALIBUT (HIPPOGLOSSUS-HIPPOGLOSSUS) AND TURBOT (SCOPHTHALMUS-MAXIMUS) YOLK-SAC LARVAE INDUCED BY BACTERIAL-INFECTIONS

Eggs of Atlantic halibut (Hippoglossus hippoglossus) and turbot (Scoph thalmus maximus) 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 unti l time of first feeding. The halibut larvae showed reduced activity an d increased mortality in response to the challenge of bacteria, compar ed to uninfected control groups. In addition, the infected halibut lar vae showed increased specific density compared to the uninfected larva e. These responses were not found for turbot. However, turbot larvae i nfected with Vibrio anguillarum had lower activity than larvae infecte d with F. ovolyticus. The reduced activity of halibut larvae occurred 1-2 weeks prior to the increased mortality, allowing infections to be detected at an early stage. The results suggest that the behaviour of fish larvae is influenced by bacterial infection.