Colonization of Vibrio pelagius and Aeromonas caviae in early developing turbot ( Scophthalmus maximus L.) larvae

Polyclonal antisera made in rabbits against whole washed cells of Vibrio pelagius and Aeromonas caviae were used for detection of these bacterial species in the rearing water and gastrointestinal tract of healthy turbot ( Scophthalmus maximus ) larvae exposed to V. pelagius and/or Aer. caviae . The results demonstrated that this method is suitable for detection of V. pelagius and Aer. caviae in water samples and larvae at population levels higher than 10 3 ml −1 and 10 3 larva −1 . Populations of aerobic heterotrophic bacteria present in the gastrointestinal tract of turbot larvae, estimated using the dilution plate technique, increased from approximately 4 × 10 2 bacteria larva −1 on day 3 post‐hatching to approximately 10 5 bacteria fish −1 16 days post‐hatching. Sixteen days after hatching, Vibrio spp. accounted for approximately 3 × 10 4 cfu larva −1 exposed to V. pelagius on days 2, 5 and 8 post‐hatching. However, only 10 3 of the Vibrio spp. belonged to V. pelagius . When larvae were exposed to Aer. caviae on day 2 post‐hatching, the gut microbiota of 5‐day old larvae was mainly colonized by Aeromonas spp. (10 4 larva −1 ), of which 9 × 10 3 belonged to Aer. caviae . Later in the experiment, at the time when high mortality occurred, 9 × 10 5 Aer. caviae were detected. Introduction of V. pelagius to the rearing water seemed to improve larval survival compared with fish exposed to Aer. caviae and with the control group. It was therefore concluded that it is beneficial with regard to larval survival to introduce bacteria ( V. pelagius ) to the rearing water.