Back to Granulocytes

These cells are have a distinctive structure and are sometimes referred to as Polymorphonuclear (PMN) leucocytes.  The cytoplasm contains numerous fine granules.

Granulocytes are assigned to different sub-populations depending on the staining characteristics of these granules in smear preparations with histological dyes (eg. Romanowsky dyes).

In fish, granulocytes are of three types: neutrophils and eosinophils are the most common while  basophils are much rarer. It is believed that basophilic granulocytes are not found in salmonids.

Notes

Distinctive structure graphic:

NEUTROPHIL: A leucocyte having no affinity for acid or basic dyes, but stainable by neutral dyes. The most abundant type of leucocyte; they are able to move out of the blood and into the tissues of the body to engulf bacteria wherever they invade.

EOSINOPHIL:  A special white blood cell (polymorphonuclear leucocyte) that can be stained with acid dyes such as eosin.  These cells are involved in destruction of internal parasites and in the modulation of allergic inflammatory reactions.

BASOPHIL: A substance or tissue element (e.g. white blood cell) showing an affinity for basic dyes; (e.g. granulocytes that can digest micro-organisms). Their numbers are normally very low in blood. There is some question as to whether such cells are present in fish.