Publication Abstract

Bacterial influences on Atlantic halibut, Hippoglossus hippoglossus L., yolk-sac larval survival and start-feed response

D. W. Verner - Jeffreys, R.J. Shields and T.H. Birkbeck

A bacteria-free halibut larval rearing system was used to test 20 bacterial isolates, previously isolated from British halibut hatcheries, for their toxicity towards halibut yolk-sac larvae under microbially-controlled conditions.

The isolates tested spanned a range of genera and species (Pseudoalteromonas, Halomonas marina, V. salmonicida-like, Photobacterium phosphoreum and V. splendidus species). A pathogen of turbot, Scophthalmus maximus L., V. anguillarum 91079 was also included. Isolates were inoculated into flasks containing 25 recently hatched axenic halibut larvae at a concentration of 5 x 102 cfu/ml, with a minimum of three flasks for each treatment.

Control survivals to 38 days post-hatch for the three experiments averaged 84, 51.5 and 49%, respectively. With the exception of V. anguillarum 91079, there was no statistically significant difference in survival between the controls and the different treatments. This suggests that most of the bacteria routinely isolated from halibut hatcheries are not harmful to yolk-sac larvae, even though most flasks contained in excess of 5 x 106 cfu/ml of the inoculated organism when the experiments were terminated. By contrast, V. anguillarum 91079 was highly pathogenic towards halibut yolk-sac larvae.

Three organisms, previously shown to inhibit growth of bacteria in vitro, were tested for their ability to protect halibut yolk-sac larvae against invasion by V. anguillarum. In four separate challenge experiments none of the test isolates, a Pseudoalteromonas strain and two Carnobacterium-like organisms, showed any protective effect.

To investigate how particular bacteria influence their start-feed response, larvae were fed axenic and gnotobiotic Artemia colonized with a range of different Vibrio sp. and examined after eight days. There were no statistically significant between-treatment differences in the proportion of Artemia-containing larvae, indicating that bacterial contamination of the live food does not appear to influence initiation of the feeding response.

Reference:

D. W. Verner - Jeffreys, R.J. Shields and T.H. Birkbeck. 2003. Bacterial influences on Atlantic halibut, Hippoglossus hippoglossus L., yolk-sac larval survival and start-feed response. Diseases of Aquatic Organisms, 56: 105-113