Search for
beneficial bacterial strains for turbot (Scophthalmus maximus L.)
larviculture
L. Huys, P. Dhert, R. Robles, F. Ollevier, P.
Sorgeloos, J. Swings-2001
Aquaculture, 193 (1-2): 25-37
Abstract:
The aerobic bacterial flora in the gut of turbot
larvae and their influence on larval survival was examined. Two turbot
experiments were run with six replicates each time. Large variation, from 0%
up to 44%, was observed in the survival percentage of turbot larvae. There
was no correlation between the number of bacteria present in the gut of
turbot larvae and the larval survival rate. During both experiments, all
replicates followed nearly the same rate of bacterial development in the gut
of turbot larvae going from circa 102 CFU larva-1 just
before first feeding at day 3 post hatch to 105 CFU larva-1
at day 9 post hatch.
In total, 127 bacterial isolates from 12 rearing
tanks were sampled for further investigation. Based on their fatty acid
profile obtained by FAME-analysis, and using principal component analysis,
the isolates were subdivided in 12 major gaschromatographic-groups or
clusters (GC-groups), 11 isolates remained unclustered. Four specific
GC-groups (namely cluster A, B, I and J) were selected as potential
beneficial bacteria for turbot larviculture as the majority of the isolates
of these clusters derived from rearing tanks with a survival percentage
higher than 35%. Representative isolates of these clusters were screened on
their ability to enhance the survival rate as well as the poor
reproducibility in larval survival in a small-scale turbot confrontation
test. Also, a Vibrio mediterranei Q40 strain, isolated from sea bream
larvae, was included in these small-scale confrontation tests. Only cluster
A and the V. mediterranei Q40 strain had a distinct positive and
reproducible effect on larval survival. In conclusion, cluster A and V.
mediterranei 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.
(Laboratory of Aquaculture & Artemia Reference
Center, Ghent University, Rozier 44, 9000 Gent, Belgium, e-mail of P.
Sorgeloos: patrick.sorgeloos@UGent.be)
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