Fish is ectothermic (cold-blooded) aquatic animal live in water, breathe dissolved oxygen, depend up on environment (water) in their body temperature regulation and usually differ anatomically and physiologically than endothermic (warm - blooded) animal and human. These differences include

1- Absence of thermoregulating centre and lymph nodes.

2- The fish are adapted for living in water where utilize the dissolved oxygen     
     through gills and swim by fins.

3- Fish have ill-developed immune system

The Percent of fish diseases in cultured fish is higher than its percent in wild fish. In Egypt, the fish farming is concentrated in north and middle delta

Aquaculture

It is

Fish culture

It is production of fish in an artificial surrounding under man control

Fish farming

It is the commercial fish production in an artificial surrounding under man control on large scale .

Fish disease

It is abnormal condition caused by infectious causes as parasitic, bacterial, mycotic and viral organisms or by non infectious causes as nutritional deficiency or genetic disorders