The current annual world production of aquaculture products is approximately 34 MMT (FAO, 1998). Farmed salmonids and shrimp represent about 1 MMT and 0.9 MMT, respectively. Total annual world-wide aquaculture landings are increasing rapidly from a total annual catch of 13.4 MMT in 1987 to 34.1 MMT in 1996. The advantages of aquaculture are numerous. Fish farmers have control of broodstock, quality of feed, the ability to harvest according to market demands, the ability to process very fresh fish close to the grow-out facility and generally exercise total quality management of the process from the raw material to the dinner plate.
However, as the aquaculture industry continues to grow, so do the problems associated with aquaculture waste. It is not only the sheer volume of waste material from the processing of farmed aquatic species but also the potential for the spread of fish bacterial and viral pathogens through the waste. Control of fish disease is a problem facing all aquaculturists and is exacerbated by the relatively high stocking densities and the close proximity of one aquaculture site to another.
The other fear is that diseases in farmed species may be spread to the wild stocks either through the waste steam or by the fact that farmed species often share the same water as the wild species.
The re-feeding of non-processed or inadequately processed aquaculture waste presents the very real possibility for the spread of disease through the feed. In some countries, mortalities are separated from other waste in order to reduce the risk of spreading infection. Of course, there is no guarantee that the waste from apparently healthy fish is free from pathogens since considerable time may be required between the contact with a pathogen and the development of symptoms.
The possibility also exists for the spread of infection through birds, which have been shown to devour contaminated waste left uncovered and then to subsequently deposit contaminated faecal material at aquaculture sites located several kilometers away.
One solution to the aquaculture waste problem is the processing into traditional by-products such as fishmeal and silage or non-traditional products such as pharmaceuticals, nutritional supplements and fine chemicals.
The present report deals with the assessment of risk and summarizes the current state of knowledge on the possibility of disease transmission through feed for farmed salmon and shrimp. Salmon was selected as an example of a cold water teleost fish, which is intensively farmed in temperate waters of both northern and southern hemispheres. Shrimp were selected as an example of a crustacean, which is farmed primarily in tropical and sub-tropical waters. Both species are intensively grown and both are prone to attack by bacterial and/or viral pathogens.
