Today, the World Health Organisation (WHO) has oriented its most important field of activity towards vaccination studies thanks to the successful vaccination applications performed in the territorial animals and mammalians.
The vaccination of the fish having a specific memory immune system for the application of vaccination in respect of evolutionary development has started in parallel to the development of the aquaculture industry.
The requirement that aquaculture should be an industry complying with the environmental conditions in addition to increasing the production and decreasing the production cost is dependent on the success of the vaccination activities. As a matter of fact, the extreme increase in the use of chemical disinfectants and antibiotics will firstly have negative impacts on the company performing this application. It will lead to a more expensive production with less quantities. Today, the most effective way in preventing such type of production losses is the successful application of vaccinations as seen in the examples such as Norway, Greece, etc. in the previous years. We have to realize a healthy production up to the world standards for ensuring a healthy development in this young industry from which we have great hopes for the future.
I. Principles of Vaccination in Fish
Aquaculture has displayed an important development in the recent 20 years. The stock abundance of trout, salmon and sea bass production is gradually increasing. This has also dramatically increased the incidence risk of diseases. The repeated use of antibiotics administered in the treatment of bacterial infections leads to not only the outcome of a resistance in these micro-organisms, but also important health problems since fish is used for human consumption. Furthermore, the disinfectants, antibiotics and similar materials used intensively increase the cost of production and cause negative impacts from economical aspects. Fish vaccines have originated with the purpose of minimizing all of these negative impacts. The vaccines that achieved important successes in some of the bacterial diseases (Vibriosis, Furunculosis, Yersiniozis) for the first time in the middle of 1970’s have attracted great interest all of a sudden in the world aquaculture since they provided easily applicable, cost-effective and long-term immunization.
The basis of vaccination depends on the principle of generating specific memory cells in the body for a specific period of time. The vaccines are composed of the preparations prepared from pathogenic organisms or their antigenic structures from which pathogenic properties are eliminated through various methods. When the vaccine is applied to the living organism planned to be protected, the memory cells generated in the immune system protect the related living organism against the same pathogen for a specific period of time.
An effective vaccine is required to have 3 main characteristics.
1. The vaccine should be safe; It is very important that its side effect should remain at minimum level and especially that it should not lead to any disease during the immunity that it provides. From this aspect, totally dead or inactivated vaccines are safer than the live vaccines. Utmost care and diligence should be paid in the use of live vaccines. Although they are attenuated, these vaccines are not avirulent. Attenuated strains can gain virulence as a result of mutations. In the recent years, progress has been achieved in the use of live vaccines in a more effective manner through the use of genetic engineering methods.
2. The vaccine should be potent; (Immunogenicity). Every microbial agent that has a pathogenic character and virulence may not necessary have an antigenic property to stimulate adequate immune response. Therefore, the agent to be selected for vaccine production (especially the strains suitable for bacterial vaccines) should bear the antigenic characters that can stimulate satisfactory immune response in the fish species to be immunized.
3. The vaccine should provide ease of production and use; The success of any vaccine that can be solely achieved in the scientific stage can gain a meaning in respect of the industry only if it can provide economic production and immunization of large quantities of living organisms.
In general, there are 3 main steps for the vaccine production in aquaculture.
1. Identification of the responsible antigen that has a property of inducing an immune reaction in the fish.
2. Production and protection of the antigen identified.
3. Generation of the responsible antigen in an immunological form through the use of various methods.
Thus, the antigen of a specific form and concentration will be transformed into a potential stimulator that can provide long-term immunization.
II. Vaccination Strategy
The time of vaccination in a plant is determined according to two important factors such as the size of the fish and the water temperature.
1. Size of the Fish: The specific immune system of the fish develop in a specific period after they hatch out of eggs in every species. For example, in salmonides, the immune system can fully develop only over a weight of 1 gram. However, minimum 4 gram of weight is required for the development of long-term immune system. This weight can vary by species. Furthermore, in the studies on the specific immune system of the sea bass species performed recently, it was stated that the specific immune system developed in the 135th – 140th days.
In practice, the producers generally prefer to immunize their fish by way of immersion when they are young. As a matter of fact, it is more economical and easier to vaccine greater quantities of fish with a little amount of vaccine and to minimize the loss of young fish. The minimum vaccination size is accepted as nearly 2 grams for gilt-head bream and Sea Bass fish. The fish that are vaccinated for the second time when they reach the weight range of 10-80 Grams become immunized against the diseases that they are vaccinated during the entire production period. In practice, the first vaccination is performed via immersion while the second vaccination is performed by way of immersion or injection method.
2. Temperature: The most important factor in fish physiology is water and accordingly the temperature of the fish. Therefore, the rate of immunological success is closely related with temperature. The lower the water temperature compared to the optimal temperature values of the related species, the slower the rate of development of immunization system. Therefore, vaccination at the temperatures that are closest to the optimum temperature values of the related species provide the quickest immunity. In general, the vaccine producers do not recommend vaccination under the degree of 5-6 C. However, in salmons, when oil-adjuvant vaccines are injected under cold water conditions, immunity develops very slowly. Accordingly, it is determined that the fish become more prepared against diseases with a developed immunity in the period when the water temperature increases and when several diseases break out. |
