Abstract
The fish inhabitant in an aquatic environment so it persists exposure to pathogen and stressor factors so they have a developing immune system similar to that in high vertebrate with some differences points. Head Kidney considered the main and primary hematopoietic organs while spleen, thymus and gut-associated lymphoid tissue represented secondary hematopoietic organs. The immune system divided to the innate immune system doesn’t have a memory of previous responses, non-specific cellular as natural killer cells, dendritic cells, neutrophils, basophils and eosinophils with non-specific component these involve complement, lysosomes and acute-phase protein, if the pathogen persists the specific, memory adaptive immunity would be stimulation which composed of two subunits humeral and natural antibodies act for invading extracellular pathogen and the second subunits which are cytokines and T-lymphocyte act for kill intracellular bacterial, parasitic and viral infection. Both subunits (innate and adaptive) of the immune system act each together in the hosts to prevent microorganism’s infection and reducer the environmental stressors and give fish immune status. It is concluded from this article review that fish, like mammalians, have an advanced immune system that plays a role in fish resistance to pathological factors and maintaining fish health.
Highlights
There was some variable features, in fish there is nobone marrow which represented the primary immune organs in other vertebrates, head kidney(HK) in fish represented the organ for hematopoietic cells, myeloid, lymphoid immune cells and produced antibodies (Ab), [4] thymus represented center for T cell maturation [5], fish lack lymph nodes, blood infiltration is done by Melan macrophage centers which is characterized by assembly macrophages combined to ellipsoid capillaries [5]
The lymphoid tissue is the main unit of immune system in fish because fish lack lymph nodes and bone marrow, there is 24.0000 fish species was morphological differences but the lymph tissue mainly consisting from reticular cells providing the innate and adaptive immunity as dendritic cells, mononuclear cells, granulocyte, mast cells, thrombocyte and natural killer cells [6]
The fish spleen composed from melanomacrophage (MMC), lymphoid tissue and surrounding with clustered ellipsoid [12], macrophage phagocytize antigen that will culminate in immune memory and represented for T lymphocyte [13], in zebra fish, spleen describes as small organ contain a large number of enitroblast at 30day post fertilization at three month the lymphoblast antigen, these developmental pattern has been detected in Catfish, Grouper and Atlantic salmon[14; 15]
Summary
Both animals (vertebrates and invertebrate) with plants have immunsystem [1] which play important function in protect themselves against pathogens[2].The immune system in fish is physiologically and functionally similar to that higher vertebrate which are mainly produce immune cells by cytokines and associated receptors is the main function against pathogen and protecting organisms against diseases [3]. There was some variable features, in fish there is nobone marrow which represented the primary immune organs in other vertebrates, head kidney(HK) in fish represented the organ for hematopoietic cells , myeloid , lymphoid immune cells and produced antibodies (Ab), [4] thymus represented center for T cell maturation [5], fish lack lymph nodes, blood infiltration is done by Melan macrophage centers which is characterized by assembly macrophages combined to ellipsoid capillaries [5]. [8] refer to variable sequence development of lymphoid organs in marine fish which as kidney ,spleen and thymus with variable function related to stage as spleen in the larval stage has erythropoitic function than hematopoietic. In teleost fish as in higher vertebrate the maternal Abs act to protect eggs against vertical transfer pathogen [11]
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