The Role Of Immunostimulants In Indian Aquaculture

*Debtanu Barman¹, Vikash Kumar², Suvra Roy², A. Sanjit Singh³, Debolina Majumder⁴, Abhay Kumar² & Atom Arun Singh⁵

¹Laboratory of Aquaculture & Artemia Reference Center, Ghent University, Belgium

²Central Institute of Fisheries Education (Deemed University), Mumbai, India

³College of Fisheries, CAU (I), Lembucherra, Tripura, India

⁴College of Fisheries, WBUA&FS, Kolkata, West Bengal, India

⁵College of Fisheries, O.U.A.T, Rangailunda, Berhampur, Orissa, India

*Corresponding author: debtanu08@gmail.com, Mobile- +32488191632

Introduction

Aquaculture is the fastest growing food production sector in the world. Among the Asian countries, India ranks second in aquaculture and third in capture fisheries. Over the last few decades, movement of animals and animal products such as broodstock, seed and feed, emergence of new diseases and their potential establishment in new area, the irresponsible use of chemical disinfectants and antibiotics are recognized as having potential impacts on environment.

Disease is major limited factor in fish culture. Epizootic ulcerative syndrome (EUS) in 1986 and White spot diseases in 1994 and other diseases like vibriosis, fin and tail rot, dropsy have had divesting impact on aquaculture production in India and Asia. An infectious disease is a major contributor to economic loose in intensive fish culture.

Farmers of India have still following semi-intensive culture system where the chances of fish in stress is more due to overcrowding and other environmental factors. Stress weakens fishes' immune systems, leading to increased susceptibility to disease.

Aquaculture faces serious problems due to various adverse effects of antibiotics such as accumulation in the tissue and immunosuppression. Moreover, due to the availability of limited vaccines in few countries and their pathogen specific protective action, much attention has been directed towards the use of immunostimulants in aquaculture to control infectious diseases.

Immunostimulation is one of the useful tools in aquaculture where vaccination and/or treatment by injections are difficult and laborious processes, and where repeated chemotherapy poses a problem of developing drug resistance strains of pathogens. Immunostimulants potentiate the immunity of the host itself, enabling it to defend more strongly against pathogens.

Definition of Immunostimulants

An Immunostimulant is a chemical, drug, stressor or action that elevates the non-specific defence mechanism or the specific immune response. Immunostimulants may be given by themselves to activate non-specific defence mechanism or may be administered along with a vaccine to activate non-specific mechanism as well as heightening a specific immune response.

List of pathogen successfully controlled by immunostimulants exposure in fish/shrimp:

Bacteria:

Aeromonas hydrophila, A. salmonicida, Edwardsiella tarda, E. ictaluri, Vibrio anguillarum, V.vulnificus , V. salmonicida, Yersinia ruckeri, Streptococcus sp.

Virus:

Infectious hematopoietic necrosis, yellow head virus, viral hemorrhagic septicemia.

Parasite:

Ichthyopthirius multifiliis

Immunostimulants used in fish and shrimp

Bacterial derivatives:-

Some bacterial component stimulate cellular and inflammatory responses in animals; logically so, as the animal are genetically and environmentally conditioned to combat these pathogens. Indeed, if the toxicity and harmful inflammatory factors are deleted, bacterial derivatives can be good Immunostimulants. For instance muramyl dipeptide (MDP), the mycobacterium peptidoglycan derivatives has been used experimentally in clinical use for immunostimulating response in cancer patients. Another Immunostimulant FK-565, a synthetic lactoyl tetrapeptide based on a component from Streptomyces olivaceogriseus sp. is known to induce stimulation against Aeromonas salmonicida in rainbow trout. Besides elevated phagocytosis, enhanced intracellular killing also observed.

Lipopolysaccarides (LPS) preparation from gram negative bacteria is used as Immunostimulant. LPS preparations have been tested in fish and are known to stimulate B cell proliferation if given in vivo or in vitro in appropriate doses. These substances are very potent even in very low doses and may occur as contaminants in bacterin preparations thus some bacterin used in fish immunizing programs may have their own Immunostimulants.

Yeast derivatives:-

Glucans, long chain polysaccharide extracted from yeast, are good stimulators of non specific defence mechanism in animals including fish and shellfish. Cultured fish and shrimp treated with these glucan have showed increased phagocytic activity and protection against some bacterial pathogens. Glucans have tremendous potential as additives in fish food for developing broad spectrum protection against bacterial disease.

Algal derivatives:-

Laminaran is a B (1, 6)-branched B (1, 3)-D-glucan, a major component in sublittoral brown algae, e.g: Phaeophyceae. Almost all B-(1, 3) D-glucan display poor water solubility which makes them less easy to handle than aqueous soluble laminaria. Laminaran obtained from Laminaria hyperhorea has immunomodulatory effect on anterior kidney. Interperitonial injection of laminaran has also been shown to be preventing mortality caused by Aeromonas hydrophila injection in Blue gourami.

Synthetic compounds:-

Muramyl peptides

Levamisole

FK-565

Animal and plant extracts:-

Chitin and Chitosan

Chitin is a polysaccharide forming the principle component of crustacean and insect exoskeleton and the cell walls of certain fungi. Rainbow trout injected with chitin showed stimulated macrophage activities resistant to Vibrio anguillarum infection.

Chitosan, de-N-acetylated chitin can increase in immunological parameters in blood such as NBT, potential killing activity, myeloperoxidase and total immunoglobulin concentration and give resistance from certain bacteria.

Vitamins:-

Vitamin C (ascorbic acid) has influence on fish macrophage function such as engulfment and destruction of bacteria. Vitamin C also neutrophils serving to inactive oxygen radicals to protect the cell from injury or promoting the oxidative destruction of bacteria. Enhanced antibody production and complement activity in channel catfish and rainbow trout due to vitamin c has been demonstrated. The role of vitamin c to enhance inflammatory response and disease resistance has been recently demonstrated in Indian major carps. Vitamin E also has shown to influence non-specific and specific defense mechanism in rainbow trout. It also plays an important role in cell membrane structure, stability and function.

Hormones:-

The relationship between neuroendocrine regulation and the immune system has recently become the subject of intense investigation. It is also known that growth hormone (GH) and Prolactin directly affect the immune competent cells (macrophage, lymphocytes....). Melanin stimulating hormone (MSH) and melanin concentrating hormone (MCH) stimulate phagocytosis by head kidney leucocytes of rainbow trout in vitro.

Time of administration of Immunostimulant

Immunostimulants may be given separately or along with a vaccine. The fish could be prepared for predicted events, such as seasonal exposure to a pathogen by a treatment prior to event. Easiest time for administration of immunostimulant and vaccine is at the same time as exposure of fish to the specific antigen. The two substances are mixed with feed or delivered through immersion. In some cases Immunostimulant is better given prior to vaccine thus helping prepare fish for antigen exposure. However, dosage and timing should for each substance should be determined.

Efficacy of Immunostimulant

Lower temperature has profound influence on the effect of Immunostimulant. So also each species, depending on its evolutionary divergence respond differently to Immunostimulant. Higher doses of Immunostimulant suppress the immune responses. Duration of administration is also important. Additionally, fish are subjected to daily and seasonal cycles that may affect the efficacy and potency of Immunostimulant.

Status of immunostimulants in India

A variety of natural and synthetic substances have been tried in Indian major carps and shrimp in India. B-1-3 glucan, levamisole, Chitosan, ascorbic acid, tuftsin, α-tocophrol and quartenary ammonium compound have been tried In Indian conditions and show immunostimulating effect on various fish.

Conclusion

The use of immunostimulants has opened a new chapter and a very promising area in aquaculture. Immunostimulants may be used to prevent looses from disease. Although vaccination is the most reliable method to control fish diseases, as yet, no effective vaccine against Bacterial Kidney disease or most viral infections and there is no single commercial vaccine available in India, and imported vaccine may not be effective because the strain which cause disease may be different in India. Immunostimulants are safer than chemotherapy and their range of efficacy is wider than vaccination. Therefore immunostimulants may be a powerful tool for controlling infectious diseases.