Fish Nutrition and Feed Technology (2+1)

Unit 12 - Feed additives

12.7.Immunostimulants
In recent years, problems with diseases have emerged as constraints to the growth of aquaculture. Increased disease occurrences and in particular the uncontrolled movement of live aquatic animals have resulted in the transfer of pathogenic organisms among countries. The shrimp culture industry of India as well as other Southeast Asian countries has suffered significant economic losses due to these viral and bacterial epizootics.

Immunostimulants are chemical compounds that stimulate the nonspecific immune system when given alone or the specific immune mechanisms when given with an antigen, thereby rendering animals more resistant to microbial and parasitic infections. Immunostimulants can be grouped as;

• Synthetic chemical agents Example: Levamisole, FK-565 a synthetic peptide
• Bacterial derivatives Example: Muramyl dipeptide (MDP), Lipopolysaccharide (LPS), Glucan, Mannanoligo saccharide
• Polysaccharides Exapmle: Chitin, Chitosan
• Animal or plant extracts (a) Animal extracts from marine tunicates and abalone have munomodulatory effects.(b) Plant extracts like Glycyrrhizin is a glycosylated saponin and saponin of soybean protein are known to have immunomodulatory effects.
• Dietary nutritional components Example: Vitamin C, Vitamin E
• Cytokines: Cytokines are polypeptides or glycoproteins which act as modulators in the immune system. Example: Prolactin, Lactoferrin
  

Immunostimulants increase resistance to infectious disease, not by boosting specific immune responses, but by enhancing nonspecific defense mechanisms. Therefore there is no memory component and the response is likely to be of short duration.