Immunostimulation of cod
larvae with a beta-glucan from marine microalgae
Aquaflow
Technical Leaflet 2003-140
European
Network for the Dissemination of Aquaculture RTD Information
(Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/
Intensively cultivated cod (Gadus morhua L.) larvae are vulnerable to stress and to outbreaks of
disease, especially vibriosis, which may kill large numbers of larvae and
juveniles. Immunomodulatory compounds are attractive for prophylactic
treatment of cultivated fish and animals, to enhance the overall resistance
againts diseases caused by pathogenic microorganisms before the specific
immune system matures and the animal can be vaccinated.
Beta (ß-1,3)-glucans are known to be
immunomodulatory, and are commercially available as e.g. Macrogard® from
yeast cell walls. The microalgal class diatoms (Bacillariophyceae
sp.) are known to accumulate large amounts of ß-1,3-glucans
(chrysolaminaran) during stationary growth phase. However, it has not yet
been documented if this glucan has immunomodulating properties, and the aim
of the study was therefore to test whether chrysolaminaran can act as an
immunostimulant for cod larvae.
Chrysolaminaran was extracted from a culture of the
diatom Chaetoceros mülleri,
bioencapsulated in rotifers (Brachionus
plicatilis) and fed to cod larvae. Two other groups were treated
similarly with Macrogard® or fed ordinary cultivated rotifers. The
immunostimulation treatments were performed at day 4, 11 and 18 after
hatching, and formulated food offered from day 20-27. At day 27, the larvae
treated with chrysolaminaran had around twice as high survival as the
Macrogard®-group and the control, and the larval growth was improved.
Macrogard®-larvae were heavily colonized by bacteria in the gut and had a
high percentage of Vibrio sp. compared to the control, whereas the bacterial numbers in
the chrysolaminaran-treated group was lower than in the control. The results
therefore suggest that chrysolaminaran had good immunomodulating effect on
first feeding cod larvae, whereas Macrogard® had no improving effects on
the larval viability. The difference between the glucans from the marine
diatom and from yeast cell walls is mainly the water solubility and degree
of branching. The positive effects from chrysolaminaran on cod larvae may be
due to this difference.
The change from live food to formulated food is a
critical stage in the first feeding, and high mortality rates are therefore
often observed during weaning phases. Measures to enhance the resistance of
the larvae against bacterial infections by non-specific immunostimulation
can be very attractive, and chrysolaminaran seems to be a very interesting
candidate for this purpose.
The Marbim (Marine bioprospecting) project is a
strategic institute program at SINTEF Fisheries and aquaculture in
Trondheim, funded by the Research Council of Norway.
For
more information:
Dr Jorunn Skjermo
SINTEF Fisheries and Aquaculture
7465 Trondheim - Norway
Tel.: +47 73 59 63 67
Fax: +47 73 59 56 60
E-mail: jorunn.skjermo@sintef.no