The development of probiotics for farmed fish is the driving force behind the new partnership between BioMar, the Department for Seafood Research of the Danish Institute of Fisheries Research, and the Danish Biotechnological Institute.
Studying the beneficial effects of reduced dietary iron and high omega-3 fatty acid levels, as incorporated into BioMar's Bio-Optimal product range, the project has the specific goal of "carrying out research on factors affecting quality of fish and fish products", says BioMar.
The Fisheries Institute undertakes projects in close collaboration with industry, universities and other institutes both in Denmark and abroad. Growth and metabolism of micro-organisms are important factors in the determination of the quality of most fresh and lightly preserved fish products.
One of the research groups at the Institute works specifically with the microbial ecology of fish products, to evaluate the presence, growth and importance of various micro-organisms, with respect to fish quality, in such areas as health hazard, spoilage and preserving effects.
While BioMar fills the role of industrial partner in the project, the Danish Biotechnological Institute contributes expertise in the required molecular biological techniques including 'in situ' hybridisation.
The Institute has worked on the use of DNA detection methods in microbiological diagnostics and epidemiology for 8 years and is involved in a number of related scientific activities.
An increasing proportion of world fish resources is being supplied by aquaculture. While the global wild fish catch has stagnated at about 90 million tonnes, the amount of farmed fish has doubled from the 10 million tonnes harvested in 1984.
But despite this significant contribution, disease remains a major problem for fish farming. Not surprisingly, as with every livestock industry, the combatting of disease is, and will remain, a vital task.
That is why the project aims to utilise natural, non-pathogenic bacteria to prevent disease in fish. This may be done either by supplying the live bacteria or by supplying nutrients or compounds that will strengthen the natural flora.
A number of traditional and modern molecular methods are being used to describe the microflora of both healthy and diseased fish, in an effort to define whether particular bacteria are associated with healthy fish.
Large numbers of bacterial cultures, isolated from fish, are also being tested for their ability to inhibit or kill fish pathogens.
The increased concern about antibiotic resistant micro-organisms spreading in the environment has led to several suggestions for disease prevention rather than disease control. One proposal the project is working on, BioMar tells FFI, is for a prophylactic method using non-pathogenic bacteria as biocontrol agents.
Several preventative measures are the focus of the current research, either aimed specifically at developing fish defence against the pathogenic organisms (vaccines) or at building a more non-specific defence against disease in general.
Although good vaccines are being developed and marketed, they cannot be used as universal disease control measures in all areas of aquaculture.
A further problem is that juvenile fish are not fully immunocompetent and do not always respond to vaccination. Vaccination by injection, sometimes the only effective route of administration, can be very impractical when applied to small fish or large numbers.
Like all organisms, fish also carry a natural, non-pathogenic bacterial flora, on the skin, on the gills and in the intestinal tract. Just as the gut-intestinal flora protects humans against many gastro-intestinal diseases, the bacterial flora of fish may also be an important line of defence against disease.
The mechanism may be that the natural flora simply occupies niches and uses nutrients that the pathogenic bacteria need; alternatively, they may participate in a more war-like drama and actively produce substances that inhibit or kill the pathogens.
Preliminary experiments with some of the selected cultures are very promising, says BioMar, and indicate that mortality can be reduced significantly by the use of bacteria that are particularly inhibitory to fish pathogens.
Parallel to the practical testing of bacteria in infection trials, molecular methods are being used to determine the ability of the probiotic bacteria to colonise the fish, thereby evaluating if a probiotic has to be supplied on a continuous basis or if a single treatment would be sufficient.
(article from Fish Farming International, 25(3), March 1998)