|a||Fisheries Research Centre, Ministry of Agriculture and Fisheries, P.O. Box 297, Wellington, New Zealand|
Received 16 June 1991; Accepted 20 September 1991. Available online 10 August 2007.
The occurrence and functions of granulocytes in fishes varies between and within groups. Primitive groups (agnathans, holocephalans, elasmobranchs) all have eosinophils with homogeneous round granules. Elasmobranchs also have eosinophils with granules containing an axial crystalline rod, which is the sole eosinophil type present in lungfish. Comparative study suggests that in elasmobranchs and lungfish, heterophils and different forms of eosinophil are all of the eosinophil lineage. Agnathans, holocephalans, dogfishes and lungfish possess fine granulocytes that may be related to neutrophils of teleosts and mammals. Holosteans and chondrosteans have eosinophils and neutrophils, and as in some elasmobranchs and lungfish, basophils are relatively common. Teleosts have neutrophils which are ultrastructurally, and possibly functionally, similar to mammalian neutrophils. More rarely they have cells with elongated granules similar to elasmobranch and reptilian heterophils. Teleost eosinophils have large round homogeneous granules, and cytochemical and functional studies indicate that in some groups, particularly cyprinids, these cells represent an undifferentiated eosinophil/basophil lineage. Roles in inflammation, enzyme cytochemistry, function and evolutionary trends are discussed.