Haemogregarina nototheniae n. sp., from the blood of Antarctic nototheniids

Abstract

A new species of haemogregarina, Haemogregarina nototheniae, is described from the Southern ocean teleosts Notothenia neglecta and Notothenia rossii. Stages identified as macro- and microschizogony and gametogony are described in mononuclear leukocytes from fish caught during the austral summer. The mature gametocyte is the most commonly found stage: it is exoerythrocytic, but carries the host erythrocyte nucleus attached to its external surface near one end. The gametocyte has a central nucleus and 2–16 subterminal eosinophilic granules, but no polar cap. During microschizogony the schizont nucleus undergoes repeated division without cytoplasmic division to give 32 nuclear masses, all of which appear to be in metaphase. Cytoplasmic division yields free merozoites identifiable by the coarse chromatin of the nuclear area. During macroschizogony the intraleukocytic parasite swells to a subspherical mass with a median band of fine heterochromatin granules. The cytoplasm later divides, forming three merozoites. There appear to be two routes by which merozoites proceed to become gametocytes: in winter small merozoites are seen in mature erythrocytes; but in summer, in erythroblasts. The invertebrate definitive host and the means of transmission are unknown, but the parasite is provisionally assigned to the genus Haemogregarina.