Changes in the gut-associated microflora during the development of Atlantic halibut (Hippoglossus hippoglossus L.) larvae in three British hatcheries

The bacterial flora of reared Atlantic halibut eggs, larvae, juveniles and adults from three different UK halibut hatcheries was monitored using a combination of traditional biochemical tests, the BIOLOG GN bacterial identification system, PCR-RFLP of 16S rRNA genes and partial 16S rDNA gene analysis. A gut microflora was detected towards the beginning of the non-feeding yolk-sac stage, with a substantial increase as the larvae started to feed. Bacteria isolated from non-feeding yolk-sac larvae were predominantly non-fermentative Gram-negative rods, in particular Pseudoalteromonas species; by contrast, the presumptive gut microflora of first-feeding larvae was generally dominated by members of the Vibrio genus. There was evidence of a bacterial succession after the larvae started to feed. Initially, first-feeding halibut reared on enriched Artemia were generally colonised by live food-associated bacteria, particularly Vibrio splendidus and V alginolyticus-type organisms. Genetically similar V splendidus isolates were recovered from enriched Artemia and the guts of first-feeding halibut larvae in all three hatcheries. However, only a selected proportion of the Artemia-associated bacteria appeared able to establish themselves within the guts of larval halibut. First-feeding halibut larvae were sometimes colonised by opportunistic bacteria. The gut floras of two individual batches of halibut larvae were briefly dominated by a Pseudoalteromonas and a Photobacterium phosphoreum isolate, respectively. Genetically-similar V salmonicida-type organisms were present in larvae sampled from all threehatcheries, both from copepod and Artemia-fed fish. The guts of the adult halibut analysed had a culturable flora dominated by Photo. phosphoreum. (C) 2003 Elsevier Science B.V. All rights reserved.