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

In principle, the only factors that need to be considered in choosing the correct design of an immunoassay are thetypes of antibodies that are available (polyclonal antibodies, monoclonal antibodies, a single or two or moremonoclonal antibodies) and whether pure or impure antigen is available.Polymerase chain reactionPCR is a technique for the in vitro amplification of specific DNA sequences by the simultaneous primer extensionof complementary strands of DNA. The reaction composes with three steps including: denaturation, annealingand extension. The final products or PCR products are subsequently analysed by agarose gel electrophoresis orwith some more advance techniques for further required information.In situ hybridizationIn situ hybridization is a technique for identifying specific nucleic acid sequences (genes) in their cellularenvironment. The probe is oligonucleotide specific to the target DNA of the pathogen/organs. The probes arenormally linked with the signal system, which can be enzymatic system or isotopic system. In final step the linkedsignal is visualized with relevant enzyme/substrate to determine the reaction.Disease prevention strategiesGood farm managementGood farm management is a major part of the disease prevention strategies. Since the infectious agents are allaround in the environment and surrounding wild aquatic animals, farmers should take a number of measures tominimize the disease in their stocks. These measures are including:• screen seed/broodstock for any infectious agents before introducing into the farms• control water source and quality to ensure optimum growing of their animals and reduce exposure topathogens• maintain stocking densities at optimum level• allow time to fallow sites between crops and apply disinfectant to pond/tank and equipment• apply strict hygiene practices including disinfection procedures• avoid equipment movement between different areas of the farms• improve nutrition and diet, and store them in cool, dry, and well-ventilated place to prevent rancid andmoulding• closely monitor the stocks to ensure early detection of disease problemsHealth surveillanceRegular monitoring of fish health is highly recommended to be part of good aquaculture practice. This will assurethe farmer to be aware of the fish health status and any early infection that may occur within their farm. Thesampling size must be well represent the whole population and minimize the overlooking of the early infection.Number of fish samples for the health surveillance purpose is described in Table 1.However, the process of capturing fish can introduce some certain degree of stress to both sampled fish and theentire population. Netting and handling should greatly be taken care and time out of water should be minimized.Anesthetics are also commonly practiced to improve fish survivability and growth post handling.VaccinationVarious types of vaccine are commercially available mainly to the major diseases of economic fish species.Monovalent vaccine is a product to cover only one pathogen strain, whereas the multivalent is aimed to cover a52