WILD FISH STOCKS It is questionable what if anything can be done to control

Wild fish stocks it is questionable what if anything

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WILD FISH STOCKS It is questionable what, if anything, can be done to control disease in wild fish stocks. Perhaps the first step should be to determine the precise extent of disease among wild fish populations. Surveys have been carried out with a view to assessing the incidence of "abnormalities" in marine fish. Indeed, some workers have attempted to correlate the incidence of disease with pollution (see Chapter 11). It is suggested that attention be focused on archive material, collected at or before the turn of the century. Such material is housed in some museums, e.g. in Liverpool, U.K., and access is usually granted to interested individuals. A detailed study would soon demonstrate whether
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338 Bacterial Fish Pathogens Table 10.1. Methods of controlling bacterial fish diseases Classification of fish stocks Disease control measures Wild Control of pollutants (water quahty) Farmed 1. Adequate husbandry practices 2. Use of genetically resistant fish strains 3. Adequate diet or, where appropriate, use of dietary supplements 4. Use of vaccines 5. Use of non-specific immunostimulants 6. Use of antimicrobial compounds 7. Water treatments 8. Preventing the movement of infected stock 9. Probiotics/Biological control or not "abnormalities" in fish are a new or old phenomenon. Surely, this information could then be correlated with the changes in pollution of the aquatic environment. It is our contention that dense populations of fish have always maintained a given level of diseased individuals, regardless of whether the populations are shoals in the sea or aquacultural stocks. Therefore, it is possible that reducing pollution will not noticeably alter the health index of wild fish. Nevertheless, by using a circuitous route, it may be possible to ensure that wild fish stocks are not likely to be exposed to pathogens, and therefore be at less risk of disease. Theoretically, this could be achieved by controlling outbreaks of disease in farmed fish and thereby reducing the possibility of pathogens escaping into the environment. It should be emphasised, however, that there is a dearth of information, which suggests that disease may be transferred from farmed to wild fish stocks. At worst, there is a perceived problem, and this could easily escalate into adverse propaganda for the aquaculture industry. It is essential that consideration should be urgently given to control measures, which will reduce any possible risk of pathogens escaping into the natural environment. FARMED FISH There are many approaches which need to be adopted in order to control bacterial disease in farmed fish (Table 10.1). These will be explained separately below. Husbandry To reiterate a previous point, it is a common problem that, under severe economic pressures, the aquaculturist is tempted to produce the maximum yield of fish in a finite volume of water. Sympathy must be addressed towards the fish farmer, es- pecially in the U.K., insofar as the prices of the principal products, i.e. Atlantic salmon and rainbow trout, have not kept pace with inflation. Smaller profit margins
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