Ensuring Good Health & Biosecurity on Fish Farms
Disease prevention is a top priority when it comes to maintaining a healthy stock. Good health starts with ensuring that only healthy and disease free fish are stocked into a clean environment. This often means carrying out health checks prior to stocking fish or shellfish onto the site using competent trained personnel. It also means buying fish from stock which have been certified as free from specific diseases.
Biosecurity is key to aquaculture success. As most aquaculture facilities rely on natural water sources – rivers, ponds, seas – it is difficult to achieve 100 per cent biosecurity. However, it is important that effort is made to ensure that no pathogens are introduced into the farm from vehicles, visitors, staff, equipment. If possible, incoming water should be treated for pathogens using ultra-violet radiation or ozone. This is usually only practically possible in hatcheries or land based recirculation systems where a relatively small volume of water is being treated. This is also the part of the production cycle where it is particularly important as juvenile fish and larval shellfish are particularly susceptible to disease.
Farm biosecurity audits and risk-assessments should be made on a regular basis and appropriate control measures put in place at each risk point. Effective hygiene and disinfection procedures must be developed at each point ensuring that the appropriate disinfectant at the required concentration and contact time is being used.
Appropriate hygienic protective clothing should be available for staff and visitors. Visitor control should include written assurance that they have not had any recent contact with other potentially infected animals. Appropriate predator and pest control must be in place as these can also present a biosecurity risk. All elements of the biosecurity programme must be adequately monitored and documented, e.g. replenishment of disinfectant foot baths on a regular basis.
A second tier of disease prevention is the use of vaccines to protect fish against specific pathogens. Many vaccines are now available against common bacterial and viral pathogens and are a vital tool in maintaining healthy stocks. Vaccines, however, should never be seen as an alternative to good management and appropriate biosecurity procedures.
Many fish and shellfish diseases are triggered by stress and poor environment and good management combined with an optimum aquatic environment and a high nutritional status are all necessary if good health is to be maintained. Many disease organisms are ubiquitous in the aquatic environment and it is impossible to eliminate them from farms. Only by ensuring optimum welfare, vaccination status and environment can the farmer ensure that his fish will be robust enough to defend themselves against pathogenic challenges.
Breaking the pathogenic cycle where management procedures reduce the level of environmental pathogens is important. This includes never stocking more than one generation of fish/shellfish in the same environment – this ensures that pathogens are not passed from one generation to another. Ensures that there is a break between harvesting and re-stocking the farm is also key, i.e. fallowing the site for a minimum time period to reduce the pathogenic reservoir in the environment or periodically moving the farm to different locations.