Occurrence ofAphanomyces ovidestruens, a fungus parasitic on copepods, in two eutrophic lakes

Abstract

Aphanomyces ovidestruens, a fungus parasitic on the calanoid copepod Boeckella dilatata, is reported from two eutrophic lakes in New Zealand. Several differences between the parasite on B. dilatata and that described originally from Diaptomus gracilis were noted: the infection hyphae on B. dilatata did not swell distally into “bulbous appressoria” and the oogonia were typically larger and ornamented with spines or tubercles. The incidence of infection among adult female B. dilatata from 1969 to 1978 varied from nil to over 20% in both Lake Hayes and Lake Johnson and reached a peak of 47.7% in Lake Hayes in October 1977. Infection was highest in winter, spring, and late summer and lowest in early summer and autumn in both lakes. In Lake Hayes, peaks of infection roughly coincided with times when numbers of adult females of successive copepod generations were waning; this implies that the incidence of infection increases with female age after maturation.