Susceptibility, copepods

Most of the work on the invasion of the first intermediate host deals with the susceptibility of different species of copepods to infection by coracidia. The evidence points to the conclusion that procercoid specificity is generally euryxenous (i.e. with a broad host spectrum). A striking example is seen with D. latum in which no less than 17 species of copepods are susceptible (59). Some species, however, show a tendency to be stenoxenous (i.e. with a narrow host spectrum), e.g. B. claviceps, with only two copepod species being highly susceptible (189). 

Measurement of susceptibility is further complicated by the fact that species of copepods which may readily be infected experimentally in the laboratory may only serve as poor hosts under natural conditions. For example, in the laboratory, Cyclops scutifer was found to be readily invaded by the coracidia of Triaenophorus nodulosus and yet in Lake Lergi, this species of copepod showed a prevalence of only 0.28% (849). This result may be due to the behaviour and/or the physiology of the coracidia or the host or both, being different under different environmental conditions. 

A study on UVR susceptibility in cod eggs was undertaken in parallel with the exposure of Calanusfinmarchicus reported above [2,4,111]. While the BWFs for cod eggs resembled that of naked DNA, and UVR effects were indeed observed under natural solar intensities, it was nevertheless concluded that cod eggs and embryos were far less susceptible to natural UVR compared with the tested copepods. While a model evaluation suggested that a more than 50% increase in damage could occur under realistic ozone depletion scenarios for Calanus, this was almost negligible for cod eggs or embryos. This does not imply that UVR is... 

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