Fish Vaccination: A Health
Management Tool for Aquaculture
Arun Sudhagar S1,
Ferose Khan2 and Linga Prabu D2
1Department of Fish Pathology &
2Division of Fish Nutrition,
Biochemistry & Physiology
Central Institute of Fisheries Education
Aquaculture has been globally recognized as the fastest growing food
production sector (FAO). The intensive farming of finfishes and shellfishes has
led to an imbalance of optimal culture conditions, which shows increased
susceptibility to infectious disease. Increased incidence of microbial diseases
in aquaculture system is the major obstacle in the success of the industry. Use
of antibiotics has attracted lot of criticism due to the issues like antibiotic
residues, bacterial drug resistance and toxicity. In this present scenario,
vaccination would be the best alternative to combat bacterial and viral disease
for the sustainable aquaculture. The first report on fish vaccination was by
David C. B. Duff and he is regarded as
"Father of fish vaccination".
Concept of vaccination
"Prevention is better than cure"
is an easy, effective and preventive method of protecting fish from diseases. Vaccination
is a process by which a protective immune response is induced in an animal by
administration of vaccines. Vaccines are preparations of antigens derived from
pathogenic organisms, rendered non-pathogenic by various means, which will
stimulate immune system of the animal to increase the resistance to the disease
on natural encountered with pathogens. Once stimulated by a vaccine, the
antibody-producing cells, called B lymphocytes, remain sensitized and ready to
respond to the agent should it ever gain entry to the body.
Importance of vaccination
are not the same as antibiotics and generally will not be effective for
stopping a disease outbreak once it has begun.
Vaccines are used to prevent a specific
disease outbreak from occurring and are not a therapy.
efficiency exists for a longer duration with one or more treatments.
toxic side effects and healthy fish have better growth performance.
of toxic residues
will not develop resistance.
it can control any bacterial and viral disease.
Characteristics of vaccine
vaccine used should be safe and should not cause toxicity to the animal.
vaccine should have high immunogenicity.
vaccine should protect the animal for a longer period. In fish, duration of one
year or life long protection can be said to be commercially effective for a
vaccine should be specific against a particular pathogen. It should not protect
or favour the other pathogens.
Types of vaccines
containing killed micro-organisms, these are previously virulent
micro-organisms which have been killed with chemicals or heat.
An Inactivated Vaccine is
culture of an infection agent on a medium and then deactivated using heat or formaldehyde.
Viruses are metabolically inert and they cannot be killed.
contain live, attenuated virus micro-organisms. These are
live micro-organisms that have been cultivated under conditions that disable
their virulent properties, or which use closely-related but less dangerous
organisms to produce a broad immune response. They typically provoke more durable
immunological responses and are the preferred type for healthy adults
inactivated toxic compounds in cases where these (rather than the
micro-organism itself) cause illness.
Rather than introducing an inactivated or attenuated micro-organism to
an immune system (which would constitute a "whole-agent" vaccine), a
fragment of it can create an immune response.
Certain bacteria have polysaccharide
outer coats that are poorly immunogenic. By linking these outer coats to
proteins (e.g. toxins), the immune system can be led to recognize the
polysaccharide as if it was a protein antigen.
A number of innovative vaccines are also in development and in use:
Vector - by combining the physiology of one micro-organism and the DNA of the other,
immunity can be created against diseases that have complex infection
vaccination - in recent years a new type of vaccine called DNA
created from an infectious agent's DNA, has been developed. It works by
insertion (and expression, triggering immune system
recognition) of viral or bacterial DNA into animal cells. Some cells of
the immune system that recognize the proteins expressed will mount an
attack against these proteins and cells expressing them. Because these
cells live for a very long time, if the pathogen
that normally expresses these proteins is encountered at a later time,
they will be attacked instantly by the immune system. One advantage of DNA
vaccines is that they are very easy to produce and store. DNA vaccination
is still experimental.
receptor peptide vaccines are under development for several
diseases .These peptides have been shown to modulate cytokine
production and improve cell mediated immunity.
- Targeting of identified
bacterial proteins that are involved in complement inhibition would
neutralize the key bacterial virulence mechanism.
- While most vaccines are created
using inactivated or attenuated compounds from micro-organisms, synthetic vaccines are composed
mainly or wholly of synthetic peptides, carbohydrates or antigens.
Vaccines may be monovalent (also called univalent) or multivalent (also called polyvalent). A monovalent vaccine is designed
to immunize against a single antigen or single microorganism. A multivalent or
polyvalent vaccine is designed to immunize against two or more strains of the
same microorganism, or against two or more microorganisms. In certain cases a
monovalent vaccine may be preferable for rapidly developing a strong immune.
Adjuvants are pharmacological or immunological agents
capable of modifying the effect of other agents, such as drugs or vaccines.
Adjuvants are virtually useless if given alone, but can serve to make a vaccine
much more effective. When given together with a vaccine, the adjuvant will stimulate
the immune system and increase its response to the vaccine. Exactly how
adjuvants work remains unknown. Aluminium salt, virosomes and certain oils are
all commonly used as adjuvants for vaccines.
There are three methods of vaccination in fish.
Injection delivery system
Injection delivery system is an
effective way of inducing antibody response in fish. The injection may be
intraperitoneal or intramuscular. But the major setbacks are, it is time
consuming, labour intensive and consequently expensive to administer to large
number of animals. During the course of injection, handling stress affects
their ability to produce optimal immune response. For safe handling and
injection, the fish should be of reasonable size. Fry cannot be vaccinated by
means of injection. Because of these limitations injection delivery system of
vaccines are used in fishes of high unit value to absorb the cost of procedure.
Immersion delivery system
Immersion delivery system of
vaccines is a potential commercial process. It is a hyperosmotic immersion
technique, where prior to immersion in antigen solution fish are dipped for a
short time in a hyperosmotic salt solution which enhances the uptake of
antigen. The advantages are, large number of fish can be vaccinated at the same
time and it can be used to vaccinate fry of any size above the critical size of
immune responsiveness. The main disadvantage of this method is the fish is
subjected to stress. Spray vaccination is a variant of direct immersion where
antigen in sprayed under pressure on to the fish, as they are propelled along a
Oral delivery system
system through feed is a potentially useful method of vaccination. Besides its
simplicity, it is a method of choice for eliciting immune response to enteric
pathogens. This method do not cause stress to the fish. It can be used to
vaccinate the fish of any size and requires no extra time or labour than normal
farm husbandry. The main limitations of this method are, to obtain effective
immunity it is necessary to give a large dose of antigen (i.e.) the total
amount of antigen needed is much more higher than injection and immersion
delivery systems and the immunity which the oral delivery system provokes is
poor and not as long lasting as injection delivery system. The poor response is
due to poor antigen delivery to immune responsive sites. Due to low pH and high
enzymatic activity the vaccine is destroyed in the foregut and causes poor
antigen delivery to hind gut and other lymphoid organs of fish. To overcome
this problem encapsulated vaccines can be used. Recently biofilm of bacterial
pathogen has been evaluated successfully for oral vaccination of fish with high
antibody tire and protection. The glycocalyx of biofilm helps to resist the
vaccine destruction in the foregut favouring better antigen delivery to immune
responsive sites in the hind gut.
How to achieve optimal effects of vaccines
efficient vaccines and administering them correctly is not the only factors affecting
the effects of vaccines. Optimal efficiency of vaccines can be achieved by proper
fish management practices. Optimal conditions and adequate nutrition are very
important and one must also strive to expose the fish to as little stress as
possible. The efficiency of a vaccine largely depends on the condition of the
immune system and exposing fish to factors that might harm their immune system
are therefore highly unadvisable.
of fish vaccines developed
yersiniosis (enteric red- mouth disease)
(enteric red-mouth disease)
of carp virus
Spring viraemia of carp
Koi herpes virus
herpes virus (KHV) disease
free-cell vaccines of Aeromonas hydrophila
Indian major carps
(group B) vaccine
in fish vaccinology
During the last two decades vaccination has become
established as an important method for prevention of infectious diseases in
farmed fish, mainly salmonid species. So far, most commercial vaccines have
been inactivated vaccines administered by injection or immersion. Bacterial
infections caused by Gram-negative bacteria such as Vibrio sp., Aeromonas sp., and Yersinia sp.
have been effectively controlled by vaccination. With furunculosis, the success
is attributed to the use of injectable vaccines containing adjuvants. Vaccines
against virus infections, including infectious pancreatic necrosis, have also been
used in commercial fish farming. Vaccines against several other bacterial and
viral infections have been studied and found to be technically feasible. The
overall positive effect of vaccination in farmed fish is reduced mortality.
However, for the future of the fish farming industry it is also important that
vaccination contributes to a sustainable biological production with negligible
consumption of antibiotics.
In addition to
optimizing husbandry and general management practices, use of vaccines is still
limited, is becoming more widespread in certain sectors of aquaculture for
disease prevention. A number of vaccines have been in use by the salmonid
industry for decades. However, commercial vaccine development for other aquaculture
sectors, including producers of warm water fish, is still quite limited.
Greater demand by producers and increased levels of research and interest by
manufacturers is helping to make vaccination a more viable option. Currently,
vaccines are available for some economically important bacterial and viral
diseases. Vaccines for protection against parasitic and fungal diseases have
not yet been developed.
Vaccination should be considered part of a comprehensive fish health
management scheme, and not the only solution for a disease problem.
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