Use Of Immunostimulants In Aquaculture Systems

Sajid Maqsood*, Prabjeet Singh, Munir Hassan Samoon and Gohar Bilal Wani.

Faculty of Fisheries, Sher-e-Kashmir University of Agricultural Science and Technology-Kashmir, India.

*Corresponding author E-mail : simplysajid@gmail.com.

The 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.

The substances of capable of stimulating immune response are the compounds that promote release of from immune effecter cells.

Immunostimulants 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.

Many 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—

1. bacteria and bacterial products,

2. complex carbohydrates,

3. vaccines,

4. immunity enhancing drugs,

5. nutritional factors,

6. animal extracts,

7. cytokines, and

8. Lectins, plant extracts.

Two main procedures for evaluating the efficiency of an immunostimulants are:

1. In vivo, eg., protection tests against fish pathogens: and

2. In vitro, eg, measurement of the efficiency of cellular and humoral immune mechanism.

Attention 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 investigated.

As 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.

Specific and non-specific immunostimulants:

Specific 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.

Non 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.

Characteristics of an ideal immunostimulants:

These can be described as:

1. It should be non-toxic, even at a high dose rate.

2. It should be non-carcinogenic or have long term side effects.

3. At therapeutic levels, it should have a short withdrawal period with low tissue residues.

4. It should stimulate a wide range of non-specific immune responses against bacteria, fungi, virus, protozoa and helminthes.

5. It should be capable of amplifying primary and secondary immune responses to infectious agents.

6. Breakdown products of compound concerned should be either inactive or readily biodegradable in the environment.

7. It should be having defined chemical composition or biological activity.

8. It should be active by oral route and should be stable both in its native state and after incorporation into food and water.

9. It should be compatible with arrange of drugs including antibiotics and anthelmintics, and

10. It should be inexpensive and either tasteless or palatable.

Objectives of immunostimulation:

These are:

1. Promoting a greater and more effective sustained immune response to those infectious agents producing subclinical disease without risks of toxicity, carcinogenicity or tissue residues.

2. Hastening the maturation of non-specific and specific immunity in young susceptible animals.

3. Enhancing the level of duration of specific immune response, both cell mediated and humoral, following vaccination.

4. Overcoming of immunosuppressive effects of stress and of those infectious agents that damage or interface with the functioning of cells of immune system.

5. 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

6. Maintaining immune surveillance at hightened level to ensure early recognition and elimination of neoplastic changes in tissues.

Some common immunostimulants:

Muramyl dipeptide: Muramyl dipeptide is a simple glycoprotein, also a purified form of mycobacteria. Its activity includes:

1. Enhancement of antibody activity.

2. Stimulation of polyclonal activation of lymphocytes, and

3. Activation of macrophages.

Levamisole: It 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:

1. enhancement of cell mediated cytotoxicity, lymphokine production and suppressor cell function, and

2. Stimulation of pathagocytic activity of macrophages and neutrophils.

Glucans: Glucans 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 against Yesinia ruckeri. Glucan treatment of Atlantic salmon (salmo salar) 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: Both 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 trout (Salvenus fontinalis) 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 immersion.

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. salmonicida infection for a short duration. It also gave protection when feeding was done @ 0.5 gm/100gm feed for one week.

Vitamin C and E: both 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.

Vitamin E 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.

Bacillus Calmette 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.

Streptococcal components: These components are potent immunostimulants. Products from Bordetella pertuosis, Brucella abortus, Bacillus subtilis and Klebsiella pneumoniae all have immunostimulating activities.

Acemannan: It 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.

Lentinan: It 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:

1. the specific and non-specific immune responses and

2. Disease resistance against Aeromonas hydrophila was investigated in Oreochromis mossambicus.

It stimulated both antibody response and neutrophil activity. Dietary intake also enhances the antibody response and disease resistance to Aeromonas. Possibility of using O. sanctum as 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 system.

Aquatim: This 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.

Aerobic coryneforms: Propionebacterium acenes promotes 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.

References

Anderson DP, Swicki AK. 1994. Duration of protection against Aeromonas salmonicida in brook trout immunostimulated with glucan or chitosan by injection or immersion. Progres. Fish Cul. 56: 258-261.

Bullock G, Blazer V, Tsukuda S, Summerfelt S. 2000. Toxicity of acidified chitosan for cultured rainbow trout (Oncorhynchus mykiss). Aquacul. 185 (3-4): 272-280.

Jeney G, Anderson DP. 1993a. Enhanced immune response and protection in rainbow trout to Aeromonas salmonicida bacterin following prior immersion in immunostimulants. Fish. Shellfish. Immunol. 3(1): 51-58.

Sahoo PK, Mukherjee SC. 1999. Influence of the immunostimulant, chitosan on immune responses of healthy and cortisol-treated rohu (Labeo rohita). J. Aquacul. Tropics 14 (3): 209-215.

Yano T, Matsuyama H, Mangindann, REP. 1991. Polysaccharide- induced protection of carp, Cyprinus carpio against bacterial infection. J. Fish Dis. 14: 557-582.