Larviculture of turbot (Scophthalmus
maximus): zootechnical, pathological and microbiological aspects
Aquaflow Technical Leaflet 2002-108
European Network for the Dissemination of Aquaculture
RTD Information (Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/
This project (launched 1996, prolonged 2000-2005),
funded by FWO-Vlaanderen (Fund for Scientific Research of the Flemish
Community), aimed to gain a better insight into the functional role of
microbiota in turbot (Scophthalmus maximus) larviculture, in order to
suppress high mortalities and decrease the use of antibiotics.
The project includes the following research items and
results:
· Influence
of antibiotics on gastro-intestinal microbiota of turbot:
A first series of experiments demonstrated that the
prophylactic use of antibiotics results in rapid resistence; antibiotics can
therefore only be applied for curative purposes.
· Microbiologically
‘matured’ water as alternative for antibiotics in turbot larviculture:
As the prophylactic applications need to be excluded,
in a consequent, empirical, approach, the culture water of turbot larvae was
colonised pre-emptively by using ‘matured water’. The objective was to
create a stable microbiological environment, which would positively affect
the survival of turbot.
· Research
of the fish pathogen Vibrio anguillarum in turbot: infection route and
pathogenicity:
Several hypotheses about the occurrence of
mortalities in turbot were verified, and the infection route of the most
important turbot pathogen was described. Results showed that the
pathogenicity of V. anguillarum is strongly serotype-dependent.
Additionally, 7 new serotypes were defined.
· Optimisation
and microbiological management of the production of live food:
The study of the infection route showed that live
food (Brachionus and Artemia) is the main vector for
pathogens. Zootechnical modifications of the culture procedure of this live
food and pre-emptive colonisation with probionts allowed improving the
hygienic quality of the turbot food.
· In
vitro
screening of probionts for inhibition of V. anguillarum in turbot
larvae, in vivo effects of a probiotic strain on digestion in
juvenile turbot, and selection of potential probionts and pathogens, and
study of microflora associated with culture of turbot larvae, live food and
turbot juveniles:
In vitro and in vivo experiments with the
associated turbot microbiota resulted in a large number of candidate
probionts that can be supplied through the live food, or directly to the
turbot larvae.
· Development
of a small-scale test for rapid evaluation of turbot probionts:
Because of this high number of selected
candidate-probionts it was impossible to check each of them separately in
large-scale turbot experiments. Therefore option was made for the
development of a small-scale standard test, allowing the selection of the
most adequate potential probionts, which can be subjected later to the final
large-scale experiments.
· Methods
for supplying probionts to juvenile turbot:
Finally a study was made how to administer (through
the fish feed) the bacteria, allowing the optimal release of the probioticum
in the intestine of the juvenile turbot. In juvenile turbot it was shown
that administration of Vibrio proteolyticus through the food
stimulated the protein digestion.
Future research will focus on testing promising
probionts at pilot scale, and will evaluate the efficiency of different
probiont formulations (lyophilisation, immobilisation, mixing with feed,
etc.).
For more information, contact
SORGELOOS Patrick
Laboratory of Aquaculture & Artemia Reference Center - Ghent University
Rozier 44
B9000 Gent
Belgium
Phone : +32-9-264 37 54
Fax : +32-9-264 41 93
e-mail:
patrick.sorgeloos@rug.ac.be