Observations on granulocyte peroxidase in New Zealand freshwater eels, Anguilla species

Peroxidase activity in the granulocytes of eels was investigated using o‐tolidine, paraphenylene‐diamine‐pyrocatechol, and 4‐chloro‐l‐naphthol as substrates, and cyanide, azide and aminotriazole as inhibitors. Most circulating neutrophils of Anguilla australis Richardson, 1848 and A. dieffenbachii Gray. 1842 showed no peroxidase activity at pH 7.6 and pH 9.0, but a few neutrophils, thought to be mature, were positive. Another granulocyte in the anterior kidney, spleen, parasitized gill tissue and, rarely, the blood contained a cyanide‐resistant, azide‐inhibited, peroxidase and was tentatively identified as the eosinophil. Neutrophils of A. anguilla (L.) showed granular peroxidase activity which was inhibited by cyanide. The eosinophil was not observed. Absence of peroxidase from most circulating neutrophils in A. anguilla and A. dieffenbachii, and its pattern in the neutrophil precursors and mature neutrophils of A. anguilla, may be due to two morphologically indistinguishable granule types. Primary peroxidase‐negative granules occur in precursors and immature neutrophils and secondary peroxidase‐positive granules in mature neutrophils of all three eels. Circulating neutrophils in New Zealand eels seldom mature and are theretore peroxidase‐negative, whereas A. anguilla neutrophils are mature and are usually peroxidase‐positive. Impairment of microbicidal activity in neutrophils lacking peroxidase is discussed.