Q40 seemed to play a role as first coloniser of the gut of turbot larvae and could prevent the colonisation of the gut by opportunistic bacteria. q 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Turbot larvae; Bacteria; Microbial management; Probiotic
1. Introduction
Considerable progress has been accomplished in the commercial culture of turbot Ž
. Scophthalmus maximus L. but larval survival remains unpredictable, especially, in the
Ž second week post hatch when mass mortalities are observed Planas, 1994; Ringø and
. Vadstein, 1998; Ringø and Birkbeck, 1999 . Experiments have suggested that these
Ž mortalities may be due to inadequate microbial conditions Minkoff and Broadhurst,
. 1994 , however, most of these mortalities could not be associated with primary or
specific pathogens but rather with opportunistic bacteria that attack the host larvae under Ž
stress conditions Olafsen, 1993; Vadstein et al., 1993; Munro et al., 1995; Verdonck .
and Swings, 1995 . Ž
Since fish larvae establish their bacterial flora partly in a non-selective way Hansen .
and Olafsen, 1990; Cahill, 1990 , the initial bacterial environment is of utmost impor- tance. In this respect, the early colonisation of the gut by non-opportunistic bacteria may
initiate a resident microflora which could prevent the proliferation and colonisation of Ž
the gut of larvae by opportunistic andror pathogenic bacteria Westerdahl et al., 1994; .
Bergh, 1995; Skjermo et al., 1997 . Colonisation of the digestive tract with beneficial or AprobioticB micro-organisms is a well-recognised practice in veterinary medicine
Ž .
Vanbelle et al., 1990 and this concept may be used in larval rearing. Ringø and Ž
. Vadstein 1998 were able to colonise the gut of turbot larvae with Vibrio pelagius when
the bacterial species was added 2 days after hatching but lower densities were observed when the larvae were exposed to V. pelagius at day 5 or 8 post hatch. Therefore, it was
concluded that V. pelagius has to compete with the microbiota already present in the larval gut for suitable attachment sites.
In the present research, the relationship between the intestinal bacterial flora of turbot larvae and larval survival rates was studied. Possible beneficial bacterial strains were
isolated to investigate their effect on larval survival. The overall goal was to identify beneficial bacterial strains that may improve the hatchery output in terms of repro-
ducibility and larval survival rates.
2. Materials and methods
