Abstract

Immunization is evolving into an important method for controlling disease problems in fish. This paper will review the immune response in fish. The methods available and proposed for introducing antigens into fish will be considered. The problems of delivering antigens in appropriate forms and concentrations will be discussed. Also, factors influencing the ability of fish to respond to antigenic stimulation will be considered.

Notes

Methods of Disease Control

1. Isolate sick fish, sanitize. Cycle water to keep it clean.

2. Administer constant therapy (not best).

3. Immunize

Immune Capabilities of Fish

1. Cell-mediated response

2. Nonspecific - very efficient - phagocytic cells. Inflammatory response exists, however, it is slower than for mammals (water temperature is low).

3. Circulating immunoglobulins

Cyclostomes - Specific Agglutinins

• immunoproteins

• high molecular weight

• secondary response?

Elasmobranchs - Specific Immunoglobulins

• 7s & 19s IgM-like (which is the primitive immunoglobulin)

Chondrostean - specific immunoglobulins 14s(6.5s) - tetramers

• secondary response

Teleosts - specific immunoglobulins

• most macroglobulins

• Tetramers, some specific second class (6.5s)

• secondary response

The anamnestic response in fish is slower and quantitatively lower compared to mammals. The duration of immunity in fish is not yet known. White blood cells of fish are produced in the haematopoietic tissue of the kidney.

Methods

1. Inject
   Advantages: stimulates sufficient circulating antibody
   -- each fish gets a standard dose of antigen
   Disadvantages- stress of handling difficult to do many fish.

2. Oral
   Advantages – Simple
   Disadvantages - difficult to standardize dose of antigen
   -- need long exposure to the antigen - antigen preparation is unstable.

3. Water exposure
   Advantages - Simple
   Disadvantages-Need long exposure to antigen
   -antigen unstable in water
   -- the agent must multiply in fish in order to get adequate antigen production

4. Osmotic exposure
   Put fish in a hyperosmotic solution such as urea or salt. This causes the lymph sinus along the lateral line to react. The fish is then put in the antigenic solution and it will absorb the antigen. 
   Advantages - Simple
   Disadvantages-only soluble antigens can be used.
   -- Fish must be handled.

Present Immunization

Vibriosis- oral whole cell bacterin

IHN disease of Salmon - attenuated live virus in water.

Environmental factors affecting immunity

1. Temperature

2. Water quality - N products
   --trace metals

3. Population density

Passive immunity

The Amazonian discus fish secretes an antibody-containing mucus. The newly hatched fry feed on this and get passive immunity. It is possible that in future, immunization of breeding stock can be done.

The Amazonian discus fish secretes an antibody-containing mucus. The newly hatched fry feed on this and get passive immunity. It is possible that in future, immunization of breeding stock can be done.

Secretory immunoglobulins

These have been little studied. They may occur, giving surface protection against opportunists such as Ichthyophthirius. Oral immunization may stimulate secretory antibody as for example it does in TGE of piglets.