September — What mussels!

Reproductive strategies of freshwater mussels

Mussels are animals in the phylum Mollusca, one of the largest groups of animals on earth. There are approximately 1000 known species of freshwater mussels in the world. The U.S. has the most species of any country, nearly 300. By contrast, Europe has a total of only 12 native freshwater mussels. With such exotic names as Mucket, Higgins’ eye pearlymussel, and Pink heelsplitter, how can you not be intrigued and drawn to these denizens of the aquatic depths? These creatures have a unique way of raising their young.

It all starts when a male releases sperm into the water. Mussels draw water in through their siphons and their gills filter out food and take up oxygen. The sperm is brought into female’s body through the siphon as well. The gametes formed from the combination of the egg and sperm are called glochidium. The glochidia are held in pouches on the female’s gills.

Ah, but the young are not content to develop within their moms. After several weeks to several months, depending on the species, the glochidia leave their cozy mommy-pouch and attach themselves to the gills of suitable fish (some mussel species are host-specific, while others are less discriminating). Here they live off of the fish, in a parasitic fashion, until such time as they are able to fend for themselves. They then detach from the host fish’s gills and settle into the river bottom where they can live for decades.

Apparently getting fish to voluntarily apply to have glochidia suck the life juices from their gills is a tough sell (actually, the fish are usually not hurt by this parasitic action) so mussels have devised ingenious ways to lure fish close enough so this responsibility can be thrust upon them.

In some mussel species the mantel tissue has been modified over time to look like minnows. By moving these tissues, passing fish are attracted and then attempt to feed on the fake “minnow.” The female releases the glochidia that then attach to the fish’s gills and their life cycle continues. In other cases (as with the snuffbox mussel and the logperch), the mommy mussel actually grabs the fish by the snout and pumps the glochidia onto the gills.

This is the time of year when this action takes place. So, grab some popcorn and a lawn chair, settle down next to your favorite mussel bed and watch the action unfold. If this is not workable, visit these websites for some great videos of this phenomenon and to learn more about these fascinating creatures of the Mississippi River: