Natural Defenses Against Infection

First line defense line against disease is skin, mucus, and other passage connection connecting internal and external environment
If the pathogen pass this first line defense, than the second line defense, which is provided by natural or innate immune mechanisms.
In this case, our own cells and the chemicals they produce seek out, identify and eliminate the pathogen.
These very general and non-specific responses are critical to the maintenance of good health.

On occasion, a pathogen can get past fish bodies’ primary protective mechanisms if it is present in very large numbers or if it has evaded or suppressed these processes.
Stronger protection is needed and we respond by mounting an acquired immune reaction specific to the pathogen.
These responses involve a variety of types of cells found in the blood and tissues, and can require a week or more to become established.
Acquired immunity consists of antibody and cell-mediated responses.


An acquired immune response can result in either short-term or long-term protection against a specific pathogen and, perhaps, against some of its close relatives.
In the case of long-term protection, re-exposure to the same pathogen weeks, months or years later reactivates the response mechanisms laid down during the original exposure.
This reactivation leads to rapid, effective elimination of the agent, often without clinical symptoms or signs of infection. When specific immunity results from unintentional exposure to agents in the environment, we refer to the resulting protection as being passively acquired immunity.


Intentional exposure to such an agent or its components through vaccination is known as actively acquired immunity
A humoral response and a cellular response. The humoral response is the stimulation of serum protein molecular synthesis homologous specific to the antigen causing the synthesis. These serum protein molecules are called antibodies

A weak bacteria will enter into the body of the fish
All potential pathogens contain antigens. The introduction of antigens by a pathogen is what stimulates the antibody response of the host
The immune system will be respond to the bacteria, and reproduce the antibody of the bacteria.


The specific immune will be produce to created future protection
The cellular response to antigen stimulation is a sensitization of cellular elements of the reticuloendothelial system.