Friday Parasite #8: A Vertebrate Parasite

A quick entry today, because I’ve got a major project due soon and I’m about to get onto a plane to go to my cousin’s wedding.

Over the past few weeks, all the parasites I’ve written about have been either arthropods or nematodes. And most of them have been organisms that plague vertebrates. So for a change of pace, here’s a parasite that is a vertebrate and plagues invertebrates: Encheliophis gracilis -- the graceful pearlfish.

                   

Pretty, isn’t it? It’s a member of a group of fish called the Carapidae. All of the Carapidae look a bit like 6-inch long eels, and most of them live inside sea cucumbers. In most cases, the pearlfish use sea cucumbers as a living shelter. During the day, they hide from larger predators in their host’s gut. At night, they swim out through the sea cucumber’s anus and forage on tiny crustaceans. But why go to all the risk of swimming around in the open water when you have a house that's made out of meat?

Pearlfish of the genus Encheliophis have evolved into true parasites. Instead of leaving their host to forage, these fish spend their lives inside the sea cucumber’s body, biting off pieces of their host’s gills and gonads whenever they get hungry. Several fish can share a host, and you might predict that large infestations could be pretty unpleasant for the sea cucumber. But here's the mystery: although sea cucumbers can eviscerate themselves when they’re threatened, and that would seem to be a simple way to kick out their parasitic tenants, it doesn't happen. Why not? Is it not worth the effort? Do the fish somehow suppress the sea cucumber's gag reflex? More research is clearly necessary.


References:
Eeckhaut, I., et al. 2004. Parasites and biotic diseases in field and cultivated sea cucumbers. Advances in sea cucumber aquaculture and management: FAO Fisheries Technical Paper 463.

Photo by John E. Randall.

Comments

[fish_hfd]

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[John]

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