Posted by Steve Parker on April 30, 2007

Q: I saw your recent article on how clams, when they are first spawned, spread by attaching themselves to fish as hosts.

Can they also attach themselves (or otherwise be spread) by water birds such as herons or commorants?

I want to put some freshwater clams in a down stream lake but don't want them to spread upstream to our larger pond with a sand swimming beach. There is at least a quarter mile between the two and the second pond is definately downgradient, but I am worried about spreading clams upstream.

Thanks!

State: New Jersey

A: Good thinking on your part as it's always best to avoid a problem altogether rather than correct one after the fact. It sounds as though you're concerned about having people step on clam shells and cut their feet. Right?

I've heard antectdotal information for years that birds can and do transport fish and other organisms on their feet but I don't know of any research that confirms this. Having said this, the immature clams that attach to fish must have a quick way to determine whether they've held on to a host that can provide food or some other kind of animal (turtle, snake, or bird) that can not support them. It does seem possible that a clam might, just might, attach to a bird's food and before it released its grip, be transported to your upper pond - I guess it could happen. My guess is, however, that it would be unusual, at best.

But more importantly, fish are especially good at moving upstream to new areas. I'm assuming that you have some kind of spillway from the upper to lower areas but even these can probably be navigated by some/all fish. So, any fish parasitized by clams in the lower area may very well access the upper area and "seed" that pond too.

I like the idea of placing some clams in your pond (I have some in mine too) but if you're concerned about the bottom for swimming, you might want to hold off on this entirely. Of course, if birds can actually transport immature clams, who knows, you may end up with them anyway. Thanks for asking and I hope this helps with your decision.

John Wiessinger ( April 30, 2007)