"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

November 3, 2010

November 3 - Telogaster opisthorchis

Previously, we met Ribeiroia ondatrae, the trematode parasite which causes limb malformation in frogs. Now meet Telogaster opisthorchis, a trematode that causes malformation in fishes, specifically the larvae of Galaxias anomalus, a freshwater fish native to New Zealand which is only found in two catchment in the Otago region. If the metacercariae of T. opisthorchis happens to lodge themselves in the right spot, they can induce spinal deformities, resulting in "kinky" fish (see photo - the top fish is normal for comparison) that, like malformed frogs, are more susceptible to predation. As you can easily imagine, even without predation pressure, the survival of such malformed fish would be heavily compromised.

Interestingly, it has been found that the parasite combined with herbicide run-off has a synergistic effect on the fish larvae. While the trematode infection alone can induce the spinal deformities, exposure to the herbicide increases the severity of malformation. In addition, snail hosts that produce the cercariae - the infective stage of T. opisthorchis which infects the fish - also release more cercariae after exposure to moderate level of herbicide. Such an example illustrates how human activities can severely alter the dynamics of pre-existing ecological processes in the environment, such as those relating to the transmission of infectious diseases.

Kelly, D.W., R. Poulin, D.M. Tompkins, and C.R. Townsend. 2010. Synergistic effects of glyphosate formulation and parasite infection on fish malformations and survival. Journal of Applied Ecology 47: 498-504.

Contributed by Tommy Leung.