Infection with the Piroplasm Haemohormidium terranovae in Relation to Haematocrit and Mortality of American Plaice (Hippoglossoides platessoides)

Abstract

The relationship between infection with Haemohormidium terranovae and the health of captive American plaice (Hippoglossoides platessoides) was investigated for over a 1-yr period. Intensity of infection and haematocrit were not significantly correlated at any of the sampling periods, although there was a moderately negative relationship between these parameters when data from all periods were pooled. Intensity and haematocrit varied inversely in time; intensities rose gradually during the winter months and dropped off significantly in the summer, while haematocrit values fell significantly until March and increased significantly by June. Only haematocrit showed a significant correlation with water temperature. Fish harboured higher intensities and lower haematocrit values prior to death than was apparent in fish that survived. The greatest differences between the mortality-group and the survivor-group occurred just prior to the greatest number of deaths, between March and June. The presence of infection in all captive plaice at all sampling periods, in the absence of leeches, is discussed in relation to possible mechanisms for long-term maintenance of infection and to possible routes of transmission of this parasite.