Fish Diseases and Management

7.6.2. Vaccination, Immunostimulants and Probiotics

Vaccination

Vaccination is the ideal prophylactic measure that can be undertaken for protecting the fish from any infectious diseases. However, owing to a shorter memory, vaccination trials in shrimp has met with only partial success. A number of formulations of fish vaccination are available and many of them are also commercially marketed. Details of vaccination have been dealt in this chapter on vaccination.

Immunostimulants

Due to the absence of specific vaccines to many diseases, other methods of prophylaxis are tried which includes use of immunostimulants, bioremediators and probiotics. fish depends on non-specific defence mechanisms more heavily for health maintenance, so immunostimulants play a significant role in the management of fish health and disease control. Immunostimulant is a chemical, drug, stressor or action that elevates the non-specific defence mechanisms by increasing phagocytosis, leucocytic activity, macrophage and neutrophil migration or specific immune response. In addition, they also reduce the immune suppressive effects of stress. Different compounds like select proteins, lipids, carbohydrate based cell wall extracts and synthetic compounds have been used as immunostimulants in farm reared fish and shellfish. The immunostimulants used in aquaculture include glucans, lipopolysaccharides, chitin, chitosan, peptidoglycans, muramyldipeptides, polypeptides, levamisole, Vitamin C, Vitamin E etc.

Probiotics

Probiotics are live microbial feed supplements, which beneficially alters the host animal by improving its intestinal microbial balance.  The probiotic microbes when administered through feed could pre-emptively colonise the gut and eliminate or minimize the pathogenic microbes through competitive exclusion process. To achieve this, probiotic microorganisms produce antimicrobial substances, compete for chemicals/ energy in the same environment, compete for adhesion sites, enhance the host immune response and increase the digestibility of ingested feed. Lactobacillus has been effectively used as probiotic in improving the general health and growth characteristics of fishes.