Training of Trainers - Library - Network of Aquaculture Centres in ...

few different pathogen strains. The application methods are also various among company, however the generalpractice are including injection, bathing, and feeding. Age and size of fish also play a role in the response to thevaccination. Vaccination at the early stage of fish normally confers a better response to the vaccine.Principle of vaccinationVaccination should be conducted in the healthy fish and where the environment is free from the diseases. Fishshould not be subjected to any kind of stress including diseases before vaccination. Things to be consideredwhen apply a vaccination scheme into the farm include fish age, vaccination method, time to vaccinate, intervalperiod between doses (if applicable) and withdrawal period before production harvest.Practical constraintsThe ideal of vaccination is to provide effective protection to fish from the target disease throughout the productioncycle. However, most vaccines have their limitation and vaccination procedure cannot avoid introducing somecertain degree of stress due to over crowding, handling, insufficient oxygen supply and anesthetic effect.Sometime, protection period cannot be planed especially to non-seasonal diseases. Vaccine cost and itsavailability are also major constraint for the vaccination scheme of aquaculture.Evaluation of vaccineEvaluation of the vaccine efficacy is mainly done by the relative percent survival (RPS).using the following formula;The calculation is madeRPS = 1- (vaccinated fish mortality% / non-vaccinated mortality%) x 100 %This method has a baseline criteria that at least 25 fish should be used in duplicate for each test population, whilethe challenge should cause at least 60% mortality in control group on the same time scale of the natural disease.The cause of mortality should be determined and non-specific infection must not exceed 10% in any group andmortality rate of vaccinated fish must be below 24% if the test is concerned to be positive (Ellis, 1988).Availability of fish vaccineVaccination has been integrated into the disease prevention strategies of the salmon and trout industries over adecade. Since these two fish species have a high marketable value, which a healthy fish stock justifies the pricepaid per vaccine dose. Some other commercial vaccines are also available such as for channel catfish, Europeanseabass and seabream, Japanese amberjack and yellowtail, Atlantic cod, and tilapia. Vaccine againstStreptococcus iniae in Asian seabass is now available, whereas other bacterial and viral vaccines are stilldeveloped.ConclusionDisease prevention strategies involve with various factors including, species economy importance, financialcircumstance and national regulation. Vaccine is one of an ideal method as its benefit is long term last. However,availability of vaccine particular to the Asian economic important fish species is rather limited. Cost of vaccinationis also the main constraint both the user and developer company. The health surveillance and good farm practiceseem to be better practical low cost measure to prevent and control the disease. However this may require atraining, which includes from know-how level to professional level. The scheme should be implemented into thenational strategies and sufficient training should be regularly provided to farmers.53