Live food is suspected to be a major source of contamination, particularly in larval rearing. A major part of live food's bacteria consists of Vibrio sp, potential fish pathogens.
Therefore it is essential to culture live food in the most hygienic conditions. General and specific disinfection procedures - such as glutaraldehyde, formol, parabens, chloramine T and natural extracts - have not shown significant results (except chloramine T), according to our tests.
For disinfection of Artemia, Inve has developed the 'DC-principle' and applied this to the Artemia DC cysts and the enrichment products DC Selco, DC DHA Selco, DC Super Selco.
This allows a 10,000 times lower bacterial contamination in the enrichment medium. Besides the above, our new enrichment product, the 'All in One Selco' is a DC product which allows, because of the 'bacteria-clean' medium, an enrichment of Artemia nauplii at a double density in the hatching tank.
For the larvae, this means there is less risk of transfer of pathogens by the Artemia and more active nauplii to withstand stress conditions.
Another approach is the use of immunostimulants to increase the non-specific immune response of the target animals. Several substances have been tested with different species of both larval and ongrown fish and shrimp.
Their effects on stress resistance, different immunological parameters and on survival after a bacterial challenge were evaluated and we found:
- Clear differences between different immuno-stimulating products;
- Selection of some immuno-stimulants which work synergetically improve the stress resistance of the animals;
- In the larval phase, immuno-stimulants can be administrated orally via enrichment of live food (eg, DIS Selco); and
- Field trials with different shrimp species, seabream, turbot, Atlantic salmon, showed that the lysozyme and hemagglutination activity of adult animals (measure the non specific immuno system activity) responded to the immunopak premix administered with the feed. The result was less mortality with or without a challenge of the tested animals.
Care should be taken using the right formulation if immuno-stimulants are included. The formula should be well balanced to cope with additional requirements for immuno-stimulated fish.
(from Fish Farming International, Vol. 25, No. 3, March 1998)