For many years, major diseases in aquaculture
were controlled by using antibiotics.
Although these substances could eliminate
the microflora of intestines and enhanced
utilization of amino acid by the host,
the usage of antibiotics posses more harmful
effect to the environment,
as well as the animal in the lower food chain
to the highest including human.
As an alternative, feed additives were introduced
including immunostimulant to replace antibiotics
against disease outbreak.
Immunostimulants are substances suitable to
be used in aquaculture feed to enhance disease
resistance against pathogenic disease
by enhancing innate immune response
What is innate immune response?
Innate immune response is the first line of
defense with non-specific antigens
The defense mechanism will response immediately
upon infection
because the components on innate immmune response
are always available in the body.
This is in contrast with specific or adaptive
immunity, which require long time between
exposure of pathogen and maximal response
as the body use this time to generate antibodies
specific for the infecting antigen
So, innate immune response is the fundamental
defence mechanism of fish.
and immunostimulants are the substances that
could enhance the innate immunity response
in fish.
It is non-pathogenic, non-toxic and do not
produce undesirable effect towards the aquatic
organisms.
Several dietary additives from chemical agents,
polysaccharides, animal and plants extracts
have been identified to be effective immunostimulants
and successfully improved resistance to non-specific
pathogens.
Immunostimulants can be administered by injection,
bathing or orally, with the latter appearing
to be the most practical.
One of the promising immunostimulants is β-glucan,
which is a naturally occurring polysaccharide
found in the cell wall of various plants (wheat,
oat, mushrooms), baker’s yeast, seaweed
and certain types of fungi.
Over the past two decades, the use of β-glucan
has been thoroughly investigated as feed supplements
in many aquaculture species.
Great survival rates were observed over fish
fed with β-glucan when challenged against
wide varieties of pathogenic bacteria
including Vibrio sp., Aeromonas sp. and Edwardsiella
sp.
Another common immunostimulants in aquaculture
were extracted from herbs and plants material
Several plants were identified to contain
medicinal values such as
mistletoe (Viscum album), nettle (Urtica dioica),
ginger (Zingiber officinale)
and chinese medicinal herbs (Astragalus membranaceus and Lonicera japonica).
Based on studies of these plants extracts,
enhanced immune response were reported in
many important aquaculture species.
For example, rainbow trout fed with mistletoe,
nettle and ginger extract showed enhanced
non-specific immune response,
Nile tilapia fed with Astragalus membranaceus
increase phagocytic activity within 1 week
after supplementation.
Besides, Higher survival rate were observed
in carp fed with Astragalus membranaceus too
following a challenge with Aeromonas hydrophilla
bacteria.
Chitin and chitosan, the polysaccharide which
constitutes the exoskeloton of insects, crustaceans
and cell wall of few fungi
are also great source of immunostimulants
Numerous research have reported the positive
outcome of chitin and chitosan to improve
protection against pathogenic bacteria infection.
Vitamins particularly vitamin C is important
micronutrients in fish feed
Besides it's function in many physiological
function,
It is also essential in regulating immune
systems.
Studies also found that increasing vitamin
C significantly increased protection against
aeromonas hydrophila in rohu.
Besides what have been mentioned here,
there are whole lots of other compounds that
have been tested and produced great effect
as immunostimulants for fish
The global interest towards immunostimulants
over conventional antibiotics are increasing,
and hopefully, this is a great movement towards
practicing sustainable aquaculture
Well, that's all for now
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