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

Disease diagnosis and prevention strategies in aquaculture includingvaccinationSuppalak LewisDepartment of Fisheries, Kasetsart University CampusBangkok, ThailandAbstractThis lecture note is aimed to produce general information of the disease diagnosis and its role in the aquaculturepractice. It is noted that it is not aimed to provide a complete procedure of diagnostic methods for aquacultureoperators, since some of those techniques involve with comprehensive procedures. However, it provides sufficientinformation to handle with the disease when it occurs within a farm. The prevention strategies and vaccination arealso described here to give a better view of disease prevention.IntroductionDisease diagnosis is a major mean to access the health status of aquatic animals in their environment. It is notconfined only to investigate the aetiology of the disease, but also to envisage the hidden threat under the water.This provides valuable information to farmers to understand their pond situation and can plan ahead to cope withthe disease when it becomes an outbreak within either their farms or regional level.It has been well understood that prevention is far better than cure. Since fish gets infection with different degreesand the sub-clinical level is often overlooked, an early detection of pathogen is one of the successful key to controlthe disease. Thus, diagnosis and routine health monitoring well serve the surveillance scheme in aquaculture.This lecture note is aimed to provide a general view of the diagnosis procedure and guideline how to preparesamples for diagnostic laboratory when it is required. The prevention strategies including vaccination are alsodescribed here as this will be an option for the farm management to reduce any loss due to the disease outbreakthat may occur.Disease diagnosisSample collectionCollection and handling of fish samples is the most critical step in order to obtain an accurate diagnosisaddressing the fish health status in a pond. Sample size is also important since it is a major factor determining theaccuracy of the method. Sample can be collected for two main purposes of diagnosis: one is for health monitoringand another is for disease diagnosis. These two purposes may cause a different size of sample collection. Ingeneral, the sample numbers should be high enough to be a representative of the population where thepercentage of prevalence is approximately estimated (see the table 1).All samples collected must be as alive or freshly dead. However, freshly dead fish are less preferable than the livefish since the changes occurring upon the death may make accurate diagnosis difficult. When fish dies, smallexternal parasite may be lost almost immediately, surrounding bacteria invade the fish and make it difficult todetermine the disease, and virus may die within a few hours. Moreover, most organs rapidly deteriorate whichmakes the fish is nearly impossible to be diagnosed by histology.48