Mercury in parasitic nematodes and trematodes and their double-crested cormorant hosts: bioaccumulation in the face of sequestration by nematodes.

Endoparasites can alter their host's heavy metal concentrations by sequestering metals in their own tissues. Contracaecum spp. (a nematode), but not Drepanocephalus spathans (a trematode), were bioaccumulating mercury to concentrations 1.5 times above cormorant hosts. Nematodes did not have significantly greater stable nitrogen isotope values (δ(15)N) than their hosts, which is contradictory to prey-predator trophic enrichment studies, but is in agreement with other endoparasite-host relationships. However, Contracaecum spp. δ(13)C values were significantly greater than their hosts, which suggest that nematodes were consuming host tissues. Nematodes were accumulating and thus sequestering some of their cormorant hosts' body burden of methyl mercury; however, they were not dramatically reducing their hosts' accumulation of methyl mercury.

In vitro culture of the avian echinostome Himasthla elongata: from redia to marita.

Axenic primary cultures of Himasthla elongata rediae harvested from hepatopancreas of naturally infected marine prosobranch snail Littorina littorea were maintained in Leibovitz's L-15 medium (osmolarity of approximately 780 mOsm, pH 7.8, temperature 14 degrees C under normal atmospheric conditions). Cultured rediae were active, motile and demonstrated high synthetic activity in metabolic labelling experiment. Long-term cultivation experiment showed 50% survival level of the rediae for up to 70 days and significant differences between mortality in redia groups derived from different host individuals. Half of the rediae in the most robust group survived for up to 163 days, when the experiment was terminated. Development and emergence of in vivo preformed cercariae and daughter rediae was observed. Cercariae in the culture also encysted, transformed into metacercariae and some of them in one to two weeks after the transformation spontaneously excysted into juvenile maritae. The employed culture system is characterized by a very low level of proteolytic activity. This system is suggested as a method permitting to obtain rediae secretory-excretory products free of host-derived contaminants.