Measures Used In Aquaculture
Of Aquaculture 2.Dept Of Fisheries Resource Manegment
of fisheries science
aquaculture has grown tremendously during the last years becoming an
economically important industry (Subasinghe et
2009). Today it is the fastest growing food-producing sector in the
world with the greatest potential to meet the growing demand for
aquatic food (FAO 2006). Globally, aquaculture is expanding into new
directions, intensifying and diversifying. A persistent goal of
global aquaculture is to maximize the efficiency of production to
disease is a primary constraint to the growth of many aquaculture
species and is now responsible for severely impeding both economic
and socio-economic development in many countries of the world.
Disease caused by Vibrio spp. and Aeromonas spp. Are commonly
episodes of mortality. When faced with disease problem the common
response has been to turn to following prophylactic measures.
following components are undertaken in prophylactic measurre for
disease prevention in aquaculture ;
are a non digestible food ingredient that beneficially affects the
host by selectively stimulating the growth and/or activity of one or
a limited number of bacteria in the colon and thus improves host
health.(Gibson and Roberfroid, 1995). In different studies since
1999, many substances have been investigated as prebiotic. Based on
the study of Mahious and Ollevier (2005), Fooks et
(1999), and Gibson et
(2004), any foodstuff that reaches the colon, e.g. non-digestible
carbohydrates, some peptides and proteins, as well as certain lipids,
is a candidate prebiotic.
non-digestible carbohydrates seem authentic prebiotics. They include
resistant inulin and oligofructose, transgalactooligosaccharides
(TOS), lactulose, isomalto oligosaccharides (IMO), lactosucrose,
xylo-oligosaccharides (XOS), soyabean oligosaccharides and
glucooligosaccharides. From in vivo and in vitro studies, inulin and
oligofructose, TOS and lactulose are presently classified as
prebiotics. IMO, lactosucrose, XOS, soyabean oligosaccharides and
glucooligosaccharides are not considered as functional ingredients
since they do not fulfill all criteria for classification as
prebiotics. Prebiotics are selectively fermented by Bifidobacteria,
Lactobacillus and Bacteroides. Inclusion of prebiotic in the diet has
been reported to increase the uptake of glucose (Breves et al., 2001)
and bioavailability of trace elements (Bongers and van den Heuvel,
later use of prebiotics, they have the binding capacity therefore
increasing the absorption of mineral such as calcium, magnesium and
iron; these minerals, are not absorbed in the small intestine and so
reach the colon, where they are released from the carbohydrate matrix
have been reported to have numerous beneficial effects in fish such
as increased disease resistance and improved nutrient availability.
The reasons for the different results are not clear yet. It may be
due to the different basal diet, inclusion level, type of
omnosaccharide, adaptation period, chemical structure (degree of
polymerization, linear or branched, type of linkages between
monometric sugars), origin of prebiotic, animal characteristics
(species, age, and stage of production), duration of use and hygienic
conditions of the experiment. If beneficial effects of prebiotics are
manifested in fishes, then prebiotics have much potential to increase
the efficiency and sustainability of aquacultural production.
Therefore, comprehensive research to more fully characterize the
intestinal microbiota of prominent fish species and their responses
to prebiotics is warranted. and survival.
origin of the term probiotic is attributed to Parker
(1974).The probiotics were defined as live microbial feed
supplements that improve health of man and terrestrial livestock. The
gastrointestinal microbiota of fish and shellfish are peculiarly
dependent on the external environment, due to the water flow passing
through the digestive tract. Most bacterial cells are transient in
the gut, with continuous intrusion of microbes coming from water and
food. Some commercial products are referred to as probiotics,
though they were designed to treat the rearing medium, not to
supplement the diet. This extension of the probiotic concept is
pertinent when the administered microbes survive in the
gastrointestinal tract. Otherwise, more general terms are suggested,
like biocontrol when the treatment is antagonistic to pathogens, or
bioremediation when water quality is improved. However, the first
probiotics tested in fish were commercial preparations devised
for land animals. Though some effects were observed with such
preparations, the survival of these bacteria was uncertain in aquatic
environment. Most attempts to propose probiotics have been
undertaken by isolating and selecting strains from aquatic
environment. These microbes were Vibrionaceae, pseudomonads, lactic
acid bacteria, Bacillus spp. and yeasts. Three main
characteristics have been searched in microbes as candidates to
improve the health of their host. (1) The antagonism to pathogens was
shown in vitro in most cases. (2) The colonization potential of some
candidate probionts was also studied. (3) Challenge tests confirmed
that some strains could increase the resistance to disease of their
host. Many other beneficial effects may be expected from probiotics,
e.g., competition with pathogens for nutrients or for adhesion sites,
and stimulation of the immune system. The most promising prospects
are sketched out, but considerable efforts of research will be
necessary to develop the applications to aquaculture.
are aquatic probiotics?
concept for aquatic probiotics is a relatively new. When looking at
probiotics intended for an aquatic usage it is important to consider
certain influencing factors that are fundamentally different from
terrestrial based probiotics. Aquatic animals have a much closer
relationship with their external environment. There are the big
differences between terrestrial and aquatic animals in the level of
interaction between the intestinal microbiota and the surrounding
environment. On the other hand, potential pathogens are able to
maintain themselves in the external environment of the aquatic
organisms and proliferate independently of the host (Hansen and
Olafsen 1999; Verschuere et al. 2000; Kesarcodi-Watson et al. 2008).
The bacterial community composition of the intestinal tract of
animals is different from that found in terrestrial animals, which
the probiotic concept was developed. Man and terrestrial livestock
undergo embryonic development within an amnion, whereas the larval
forms of most fish and shellfish are released in the external
environment at an early ontogenetic stage. These larvae are highly
exposed to gastrointestinal microbiota-associated disorders, because
they start feeding even though the digestive tract is not yet fully
developed (Timmermans 1987), and though the immune system is still
incomplete (Vadstein 1997). Thus, probiotic treatments are
particularly desirable during the larval stages (Gatesoupe 1999). The
resident microbes benefit from a fairly constant habitat in the GI
tract of man and terrestrial livestock, whereas most microbes are
transient in aquatic animals (Moriarty 1990). These animals are
poikilothermic and their associated microbiota may vary with
temperature changes. Salinity changes in the rearing environment will
also affect the microbiota and marine finfish are obliged to drink
constantly to prevent water loss from the body. A consequence of the
specificity of aquatic microbiota is that the most efficient
probiotics for aquaculture may be different from those of terrestrial
species (Gatesoupe 1999; Kesarcodi-Watson et al. 2008). Defining
probiotics is a challenge – even more so for aquaculture
application. Historically, probiotics were defined according to their
expected benefits or improvement to the host’s intestinal balance.
Being concerned with humans and terrestrial animals, probiotics were
generally Gram-positive obligate or facultative anaerobes, mostly
LAB. Based on the intricate relationship an aquatic organism has with
the external environment when compared with that of terrestrial
animals, the definition of probiotics for aquatic animals was
modified at the end of the last century.
Verschuere et al. (2000) defined aquatic probiotics as "Live
microorganisms that have a beneficial effect on the host by modifying
the microbial community, associated with the host, by ensuring
improved use of the feed or enhancing its nutritional value, by
enhancing the host response towards disease, or by improving the
quality of its ambient environment". This implies a much wider
range of microorganisms being used as probiotics for aquaculture
animals that for terrestrial animals. The above definition is a more
holistic and most appropriately defines probiotics for aquaculture.
that currently used in aquaculture industry include a wide range of
taxa – from Lactobacillus, Bifidobacterium, Pediococcus,
Streptococcus and Carnobacterium spp. to Bacillus, Flavobacterium,
Cytophaga, Pseudomonas, Alteromonas, Aeromonas, Enterococcus,
Nitrosomonas, Nitrobacter, and Vibrio spp., yeast (Saccharomyces,
Debaryomyces) and etc. (Irianto and Austin 2002; Burr et al. 2005;
Sahu et al. 2008).
probiotics are mainly of two types:
which can be blended with feed and administrated orally to enhance
the useful microbial flora of the gut .
can proliferate in water medium and exclude the pathogenic bacteria
by consuming all available nutrients. Thus, the pathogenic bacteria
are eliminated through starvation (Nageswara and Babu 2006; Sahu et
first type probiotics are using mainly in finfish aquaculture and the
second type in shrimp aquaculture. Commercially available probiotics
include pure strains, defined mixture of specific strains, but also
consortia of strains and undefined mixtures. Generally, probiotics
proposed as biological control agents in fish aquaculture are applied
in the feed or as a water additive supplement.
probiotics are marketed in two forms:
dry probiotics that come in packets can be given with feed or applied
to water. They have many benefits, such as safety, easy using, longer
shelf life and etc. (Decamp and Moriarty 2007);
hatcheries generally use liquid forms which are live and ready to
act. These liquid forms are directly added to hatchery tanks or
blended with farm feed. The liquid forms can be applied any time of
the day in indoor hatchery tanks, while it should be applied either
in the morning or in the evening in outdoor tanks. Liquid forms give
positive results in lesser time when compared to the dry and spore
form bacteria, though they are lower in density (Nageswara and Babu
are no reports of any harmful effect for probiotics but it is found
that the biological oxygen demand level may temporarily be increased
on its application; therefore it is advisable to provide subsurface
aeration to expedite the establishment of probiotics organisms. A
minimum dissolved oxygen level of 3% is recommended during probiotics
treatment. The development of suitable probiotics for aquaculture is
not a simple task. It requires empirical and fundamental research,
full-scale trials as well as the development of appropriate
monitoring tools and production under stringent quality control. A
performing mixture of probiotic strains can be designed after
evaluating the ability of individual strains to grow in low/high
salinity under micro-aerophilic or anaerobic conditions, produce
various enzymes, and more importantly, produce a range of inhibitory
compounds (Decamp 2004).
vaccine is any biologically based preparation intended to establish
or to improve immunity to a particular disease or group of diseases.
Vaccines have been used for many years in humans, terrestrial
livestock, and companion animals against a variety of diseases.
work by exposing the immune system of an animal to an "antigen"—a
piece of a pathogen or the entire pathogen—and then allowing time
for the immune system to develop a response and a "memory"
to accelerate this response in later infections by the targeted
disease-causing organism. Vaccines are normally administered to
healthy animals prior to a disease outbreak.
analogy used for vaccines is that of an insurance policy (Komar et al
2004). A vaccine, if effective, can help prevent a future disaster
from being a major economic drain. But vaccines, like insurance, have
a premium, or cost. The producer must weigh the cost in materials and
labor against the risk and cost of a disease outbreak to determine
whether vaccination is warranted. When actual vaccine effectiveness
is also unknown, this makes decision-making even more difficult.
Consultation with a fish veterinarian or other fish health specialist
will be helpful when examining cost vs. benefit of a particular
safe for the fish, the person(s) vaccinating the fish, and the
against a broad strain or pathogen type and gives 100% protection;
long-lasting protection, at least as long as the production cycle;
effective in a number of fish species;
cost effective; and
readily licensed and registered (Grisez and Tan 2005).
are the different types of vaccines?
are many different types of vaccines, and new kinds are continuously
under development. Of the types currently in use, the most common are
vaccines comprised of killed, formerly pathogenic bacteria. Bacterins
stimulate the antibody-related portion of the immune response (i.e.,
the humoral immune response).
attenuated vaccines are comprised of live micro-organisms
(bacteria, viruses) that have been grown in culture and no longer
have the properties that cause significant disease. Live attenuated
vaccines will stimulate additional parts of the immune system (i.e.,
a cell-mediated, as well as a humoral [antibody] response).
vaccines comprised of toxic compounds that have been inactivated, so
they no longer cause disease. An example, used in humans, is the
tetanus toxoid vaccine.
vaccines are made from a small portion of a micro-organism
(rather than the entire micro-organism) that ideally will stimulate
an immune response to the entire organism.
types of vaccines in development use even more modern strategies.
Examples include recombinant vector vaccines, which combine
parts of disease-causing micro-organisms with those of weakened
microorganisms, and DNA vaccines. Recombinant vector vaccines allow a
weak pathogen to produce antigen. DNA vaccines are composed
of a circular portion of genetic material that can, after being
incorporated into the animal, produce a particular immune-stimulating
portion of a pathogen (i.e., antigen) continuously, thus providing an
"internal" source of vaccine material. Other vaccine
strategies are also undergoing research and development.
are vaccines given to fish?
are administered to fish in one of three ways: by mouth, by
immersion, or by injection. Each has its advantages and
disadvantages. The most effective method will depend upon the
pathogen and its natural route of infection, the life stage of the
fish, production techniques, and other logistical considerations. A
specific route of administration or even multiple applications using
different methods may be necessary for adequate protection.
in direct delivery of antigen via the digestive system of the fish.
It is the easiest method logistically because feeding is a normal,
ongoing part of the production schedule. Stress on the fish is
minimal, and no major changes in production are required. Prior to
feeding, vaccine is mixed, top-dressed, or bioencapsulated into the
feed. To reduce leaching into the water and/or to provide some
protection against breakdown of the vaccine by the fish's digestive
processes, a coating agent is often used. For small fish (e.g., 1-5 g
or less), bioencapsulation may be a preferred method of oral
delivery. Live food (rotifers, brine shrimp) is added to a
concentrated vaccine solution, and allowed to take up vaccine. This
live food is then fed to fry or small fingerlings. Although oral
vaccine is the most preferred method, it conveys relatively short
immunity (compared to the other methods) such that additional
vaccination may be required. In addition, because of the problems
involved with getting the vaccine intact through the intestine and
adequately stimulating the immune system, there are few commercial
oral vaccines available (Komar et al. 2004).
immune cells located in the fish's skin and gills to become directly
exposed to antigens. These immune cells may then mount a response
(e.g., antibody production), thus protecting the fish from future
infection. Other types of immune cells in the skin and gills carry
antigens internally, where a more systemic response will also
develop. Immersion vaccination occurs by dip or by bath. Dips are
short, typically 30 seconds, in a high concentration of vaccine.
Baths are of longer duration—an hour or more—and in a much lower
concentration of vaccine. In practice, dips are logistically more
practical for large numbers of small (1- to 5-g) fish. Unfortunately,
protection using immersion methods may not last long and a second
vaccination may be required (Komar et al. 2004) because smaller,
younger fish may have immature immune systems and because this is a
more indirect route.
direct delivery of a small volume of antigen into the muscle
(intramuscular (IM) injection) or into the body cavity (intracoelomic
[ICe= intraperitoneal or IP] injection), allowing for more direct
stimulation of a systemic immune response. Injection vaccines
normally include an oil-based or water-based compound, known as an
adjuvant, that serves to further stimulate the immune system.
Injection is effective for many pathogens that cause systemic
disease; and protection—6 months to a year—is much longer than by
other methods. Every fish in the population is injected, giving more
assurance to the producer. Another advantage is that multiple
antigens (for different diseases) can be delivered at the same time.
However, vaccination by injection is logistically the most demanding
of all three methods. Fish must be anesthetized to minimize stress.
Injection requires more time, labor, and skilled personnel. The
correct needle size is important. The vaccine may incite a more
severe reaction if it is injected into the wrong portion of the fish.
And finally, smaller-sized fish (under 10 g) may not respond well to
this method (Komar et al 2004).
vaccines been used in fish?
have been used in food fish, in particular the salmon industry, for
approximately 30 years, and are believed to be one of the main
reasons that salmon production has been so successful. Vaccination of
salmon also dropped the industry's use of antibiotics to a mere
fraction of its original use (Sommerset et al 2005). In Norway, for
example, in 1987, before widespread use of vaccines, approximately
50,000 kg of antibiotics were used. By 1997, when vaccines had become
more routine, antibiotic usage had dropped to less than 1000-2000 kg
(Sommerset et al. 2005).
contribution of aquaculture to fish production is steadily
increasing. The increase would have been much more but for the major
constraint of loses in culture production, particularly of shrimp,
due to diseases. In India, the loss of shrimp production during
1995-96 due to diseases is estimated to be Rs.600 crores and the
loses continue around this level sine then. Loses in production of
cultured shrimp have led to the realization that the goal of
aquaculture is not merely to increase production but to make it
sustainable. In recent years the application of vaccination in
respect to finfish and immunostimulants in respect of shrimp/finfish
for disease management in aquaculture is being increasingly
recognized. Generally, immunostimulants enhance individual components
of the non specific immune response but this does not always
translate into increased survival. I addition, immunostimulants fed
at too high dose or for too long can be immunosuppressive.
substances of capable of stimulating immune response are the
compounds that promote release of from immune effecter cells.
enhance the humoral and cellular response in both specific and
non-specific ways. These agents are widely used for impaired immune
function and to stabilize the improved immune status. The use of
immunostimulants in fish culture or in aquaculture of other species
for prevention of diseases is a promising new development. In
general, immunostimulants comprise a group of biological and
synthetic compounds that enhance the non-specific defense mechanisms
in animals, thereby imparting generalized protection. This protection
may be particularly important for fish that are raised in or released
into environments where the nature of pathogen is unknown and
immunization by specific vaccine may be futile. Several
immunostimulants have been evaluated in fin fishes.
occasions arise in the course of fish culture that calls for
enhancement of immune response. These include strengthening of the
normal immune response in order to enhance protection and reduce
immunosuppressive conditions. Immunostimulants can be classified into
several categories by their origin and mode of action—
bacteria and bacterial
immunity enhancing drugs,
Lectins, plant extracts.
main procedures for evaluating the efficiency of an immunostimulants
eg., protection tests against fish pathogens: and
In vitro, eg,
measurement of the efficiency of cellular and humoral immune
is focused on the lymphocyte proliferation test as an adequate method
for providing a correct evaluation of the cellular immune condition
which can be adopted together with the more commonly used parameters,
such as phagocytosis and respiratory burst. It may be mentioned here
that the use of immunostimulants in the diets of marine fish and the
evaluation of their effect on the immune system of fish has been
immunostimulants, as such, which can be useful in preventing diseases
in land based aquaculture, in pens and hatcheries rarely occurs alone
in the natural environment, the subject deserves a discussion here.
and non-specific immunostimulants:
immunostimulation is related to the potentiation of the host's immune
system towards a unique specific antigen. Vaccination is perhaps the
best example of producing specific immunity.
specific immunostimulation generally is an attempt to upgrade
immunologic capabilities at a time when an animal may be exposed to
one or several pathogens and/or be immuno-compromised.
of an ideal immunostimulants:
These can be described as:
It should be non-toxic,
even at a high dose rate.
It should be
non-carcinogenic or have long term side effects.
At therapeutic levels, it
should have a short withdrawal period with low tissue residues.
It should stimulate a wide
range of non-specific immune responses against bacteria, fungi,
virus, protozoa and helminthes.
It should be capable of
amplifying primary and secondary immune responses to infectious
Breakdown products of
compound concerned should be either inactive or readily
biodegradable in the environment.
It should be having defined
chemical composition or biological activity.
It should be active by oral
route and should be stable both in its native state and after
incorporation into food and water.
It should be compatible
with arrange of drugs including antibiotics and anthelmintics, and
It should be inexpensive
and either tasteless or palatable.
Promoting a greater and
more effective sustained immune response to those infectious agents
producing subclinical disease without risks of toxicity,
carcinogenicity or tissue residues.
Hastening the maturation of
non-specific and specific immunity in young susceptible animals.
Enhancing the level of
duration of specific immune response, both cell mediated and
humoral, following vaccination.
immunosuppressive effects of stress and of those infectious agents
that damage or interface with the functioning of cells of immune
Selectively stimulating the
relevant components of the immune system or non-specific immune
mechanism that preferentially confer protection against
micro-organisms. For example via interferon release, especially for
those infectious agents for which no vaccines currently exists; and
surveillance at hightened level to ensure early recognition and
elimination of neoplastic changes in tissues.
dipeptide is a simple glycoprotein, also a purified form of
mycobacteria. Its activity includes:
Enhancement of antibody
Stimulation of polyclonal
activation of lymphocytes, and
Activation of macrophages.
is an anthelmintics chemical that has been shown to have some
stimulating effect on the immunological reactivity of animals and
humans. Activities of this agent are:
enhancement of cell
mediated cytotoxicity, lymphokine production and suppressor cell
Stimulation of pathagocytic
activity of macrophages and neutrophils.
are the most popular immunostimulants used in aquaculture. It is
derived from yeast cell wall and from certain higher plants. It has
excellent immunostimulatory properties and works well when injected
or fed to fish.
Yano et al. (1991) showed
that î3-1, 6, branched î3-1, 3 Glucans were effective in carp.
Jenny and Anderson (1993) showed that the use of Glucans increased
activity in non-specific defense mechanism and in protection
Glucan treatment of Atlantic salmon (salmo
induced protection against Vibrio salmonicidia.
Several Glucan products such as vitastim, macrogard, are marketed
commercially and are used in supplementing fish feeds.
chitin and chitosan have a major role in aquaculture. They are
non-specific immunostimulators which are effective on a short term
basis. Anderson & Swicki (1994) administered chitosan to brook
by injection and immersion and found that high levels of protection
occurred 1, 2, 3 days afterwards, but protection was greatly reduced
by day 14. Injection of chitosan was also more effective than simple
Actually chitosan is a
deacetylation product of chitin. The influence of chitosan on immune
response of healthy and cortisol treated rohu was demonstrated. After
treatment with chitosan sufficiently higher responses in almost all
assays of non-specific immunity was observed in comparison to their
healthy control or cortisol treated counterparts respectively without
chitosan treatment (Sahoo and Mukherjee, 1999). In aquaculture,
chitosan has been used as an immunostimulant for protection against
bacterial disease in fish, for controlled release of vaccines, and as
a diet supplement (Bullock et al., 2000). Similar dose of chitosan in
brook trout has been shown to be immunopotent. It had a higher degree
of protection against A.
for a short duration. It also gave protection when feeding was done @
0.5 gm/100gm feed for one week.
Vitamin C and
the vitamins are antioxidants. Vitamin C acts as a multiple cell
stimulator. Diet supplemented with vitamin C gave protection
against A. salmonicida in Atlantic salmon.
stimulates B and T lymphocytes: The
mode of action of vitamin E in enhancing immunity is nuclear but it
has been found that supplemental vitamin E may serve as a significant
stimulus of immunity in some individuals.
Guarine (BCG): It
is a potent cytokine synthesis enhancer. It is actually a live
attenuated vaccine strain of Mycobacterium bovis. BCG produces a
generalized enhancement of both B cell and T cell mediated responses
of phagocytosis and resistance to infection.
components are potent immunostimulants. Products from Bordetella
pertuosis, Brucella abortus, Bacillus
subtilis and Klebsiellapneumoniae all have
is a complex carbohydrate. It is a potent cytokine synthesis enhancer
with anti-tumor and anti-viral activities. It also has the important
property of stimulating wound healing.
is a polysaccharide extracted from a comestible mushroom. Lentinus
elodes is endowed with anti-tumor activity. Lentinan might act
by increasing sensitivity to histamine and serotoxin.
Leaf extract of
Ocimum sanctum: Effect
of leaf extract Ocimum sanctum on:
the specific and
non-specific immune responses and
investigated in Oreochromis
It stimulated both antibody
response and neutrophil activity. Dietary intake also enhances the
antibody response and disease resistance to Aeromonas.
Possibility of usingO.
immunostimulant is used in the maintenance of finfish health in
intensive freshwater aquaculture/
C-UP 111: It
has immunostimulant activating leucocyte functions. Highest
preventive effect has been shown against Aeromonas infection
in Nile tilapia with improved neutrophil function, in comparison with
Glucans and lactoferin. It is the most popular agent in aquaculture
is a kind of immunostimulant developed by the department of
Microbiology of the College of Fisheries, Mangalore and now
manufactured and marketed by Mangalore Biotech Laboratory, Mangalore
under this trade name. It is widely marketed in India, particularly
in Karnataka and Goa.
antibody formation when administered as a killed suspension. This
bacteria is phagocytosed by macrophage and stimulates cytokine
synthesis. This organism has a general immunostimulating action
leading to enhanced antibacterial and antitumor activity.
Roberfroid MB (1995). Dietary modulation of the human colonic
microbiota: introducing the concept of prebiotics. J. Nutr. 125:
Mahious AS, Ollevier
F (2005). Probiotics and Prebiotics in Aquaculture.1st Regional
Workshop on Techniques for Enrichment of Live Food for
Use in Larviculture-2005, AAARC, Urmia, Iran. p. 67.
Fooks LJ, Fuller R,
Gibson GR (1999). Prebiotics, probiotics and human gut microbiology.
Int. Dairy J. 9: 53-61.
Gibson GR, Probert
HM, Van Loo J, Rastall RA, Roberfroid MB (2004). Dietary modulation
of the human colonic microbiota: Updating the concept of prebiotics.
Nutr. Res. Rev. 17: 259-275.
Breves G, Sztkuti L,
Schr˛der B (2001). Effects on oligosaccharides on functional
parameters of the intestinal tract of growing pigs. Deutsche
Tierarztliche Wochenschrifte 108: 246-248.
Bongers A, van den
Huevel EGHM (2003). Prebiotics and the bioavailability of mineral and
trace elements. Food Rev. Int. 19: 397-422.
Parker, R.B., 1974.
Probiotics. The other half of the antibiotic story. Anim. Nutr.
Seafood — Fish — Crustacea
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