Nature Blog Network

Tuesday, August 26, 2008

Bivalve vs. Fish

This one is for the folks who thought bivalves are "boring benthic creatures" that just sit around like a lump on or in the substrate...

This is the Snuffbox Mussel (Epioblasma triquetra), a member of the Family Unionidae, the freshwater pearly mussels. Unionidae larvae (glochidia) are ectoparasites on the gills of fish. Getting the glochidia on the fish gills can be tricky and a variety of methods have evolved within the Unionidae. One general method is to get the fish close, real close, then "spit" your larvae into their face so they breath them in and across the gills. (one of my son's favorite Parasite Unleashed cards) The Snuffbox (and several other species) takes this to an extreme by actually clamping onto the fishes head, then pumping water and glochidia into the now gasping fishes throat. Even within this general method there is huge variation, with adaptations of shell shape, mantle and specialized glochidia brood pouch (marsupial gill). The following video is from M.C. Barnhart showing the capture of a logperch (Percina caprodes) and then the glochidia being pumping into its gills.


  1. Why are the freshwater bivalves so often parasitic? I recall it having to do with limited availability of dissolved mineral in freshwater. Something about using the fish juices to get what they need for shell formation. But I forget if that's accurate. Are there parasitic saltwater bivalves?

  2. I am sure there are parasitic saltwater bivalves, just don't know off the top of my head right now.

    But your other question, fish have a lot of calcium in their muscle, which might be a limiting nutrient in freshwater. I wonder if shell thickness and growth rate is faster for parasitic freshwater bivalves than for free-living ones (controlled for age).

  3. whatever the original cause, I would think that the parasitic nature also provides a somewhat controlled dispersion and more protection from predation compared to a planktonic or benthic free living stage.


    (was that out of place?)

  5. This form of 'host-capture' is unique to the genus Epioblasma. The edge of the shell is actually serrated and many fish that get caught by it are probably killed. Fourtunately, the log perch has a super tough skull and can withstand the clamping. Not suprisingly, the log perch is the only known host for the snuffbox.

  6. I would side with the dispersion theory myself.
    I had a bunch of amur bitterlings (Rhodeus sericeus) and an Anodonta bivalve in my aquarium a long time ago. Actually, that's how I started my tank-keeping career that's on pause right now. But I digress. I observed the spawning event, where female would hoist her eggs into the mussel through a long ovipositor. A dominant (colorful!) male would then swoosh down and eject sperm into the intake of the mussel. I was told that at that time, mussels can eject their larve - spit into their face, as already mentioned. Because I didn't have a pair of mussels (I don't think they're hermaphrodites?) and lack of planktonic food in the tank, I didn't see the mussel spawning event.

    Now if you'll excuse me, I have a spider to find. Already got three mosquitos and it would be a waste to throw them away.

  7. Several species in the Subfamily Anodontinae are hermaphoroditic and some actually bypass the host stage as well.

    You bring up another interesting topic of the fish turning the tables on a mussel. Instead of the mussel doing the parasitizing, the bitterling is doing parasitizing. For an interesting read this relationship, I suggest

    Reichard et al. 2007. A possible evolutionary lag in the relationship between freshwater mussels and European bitterling. Journal of Fish Biology. 70, 709-725 (Am I allowed to cite a fish paper on this blog?!)

  8. This paper is about a vert-invert interaction so 100% OK. Looks very interesting actually.

  9. Ouch, fish parasitizing a mussel! That's an interesting turn... gotta read that paper now...

    Most Unionidae are dioecious, but then in Reproductive Strategy of the Freshwater Pearl Mussel Margaritifera margaritifera G. Bauer reports that at least one species, while usually dioecious, in low densities, many females will switch to become simultaneous hermaphrodites.

    Hopefully soon I can do a survey of Unionidae glochidia dispersion techniques... there are some rare beauties in there.

  10. For a good review of at least a subset of Unionidae glochidia dispersion techniques, check out

    Zanatta&Murphy. 2006. Evolution of active host-attraction strategies in the freshwater mussel tribe Lampsilini. Moleculare Phylogenetics and Evolution. 41(2006)195-208

    Barnhart, Haag, Roston. 2008. Adaptations to host infection and larval parasitism in Unionoida. J North American Benthological Society. 27(2)370-394

  11. Thanks for the references! More great reading to do.

  12. Jive...hell no it's not out of place. If Kevin can do LOL! Scallops you can do LOL! Mussels.


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