The biology of two Eimeria species (Protista: Apicomplexa) in their mutual fish hosts in Ontario

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Abstract
Eimeria degiustii and E. iroquoina were studied in natural infections of their mutual cyprinid hosts the common shiner, Notropis cornutus, and the fathead minnow, Pimephales promelas. Experimental infections involved lab-reared fathead minnows. Oocysts were acclimated to different temperatures to investigate the effects upon the parasites' development and infectivity.Eimeria degiustii occurred at 21% prevalence in common shiners 2 years of age or older. Development was parenteral. Gametogony was recorded during the winter in the spleen and oocysts were found primarily in this site.Viurtally all Notropis cornutus 4 to 5 weeks of age were infected with E. iroquoina. Fish 1 year old or older act as reservoirs of infections with about 30% prevalence. Eimeria iroquoina develops in the intestinal epithelium, primarily immediately posterior to the bile duct. During the winter autoinfection of the posterior intestine possibly occurs. Transmission of E. iroquoina from N. cornutus to P. promelas demonstrates this parasite's lack of rigid host specificity.Eimeria degiustii and E. iroquoina appear to minimize competition in mutual hosts by infecting different age-classes in different sites and by forming oocysts primarily at different times of year. Eimeria iroquoina is transmitted directly. Eimeria degiustii probably requires an invertebrate intermediate host.

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