Pond Boss Forums GENERAL QUESTIONS Help Black spot

I've got black spots on thr blue gills, we also have herons and king fisher. What to do in our 1 acre Illinois rural pond?

As you may be aware, the trematode parasite that you are referring to has a complex life-cycle that involves a fish eating bird, a snail and the fish. The key for control is to disrupt the transmission dynamics. Killing the fish would work but defeats the purpose. Killing the birds would work until more showed up, but it is illegal anyways. Your focus should be on the snails. Controlling the snails equates to controlling both the prevalence and intensity of infection. Molluscides are available, but the most practical way is to stock redear sunfish. Redears readily eat snails, that's why they are commonly referred to as "shell-crackers".

If you stock them, make sure they are large enough that they won't get eaten by any predatory fish that you might have swimming around (largemouth bass). This approach won't totally solve your problem, but its a good start. It will also give you an additional species to catch. Good luck.

I was just wondering Shawn, would that cycle apply just to snails or any shell fish such as mussels?

Great question. When the trematode egg hatches, the parasite is in a developmental form called the miracidium. This little critter swims around until it perishes or if it gets lucky and finds its host. They have been known to find mussels, but it is rare. I suppose this would be because the mussel would have to have some soft tissue being exposed at exactly the right time. Further, some of these parasites are very host specific. In some situations, just finding a snail is not enough. It must be the snail of a particular genus or even species.

I just pulled out a reference book, and learned that the snail needed for black spot (Uvulifer ambloplites) belongs to genus Helisoma. It makes no mention of freshwater mussel hosts. However, just because it has not been reported does not mean that it cannot/does not happen. As a rule of thumb, though, most of the fish parasites (trematodes) are known to almost exclusively use snails. In this case, I'm going to predict that it doesn't use a mussel. The reason I say this is because it is very specific to snails in just one Genus. This would leave me to think that experiments have been conducted with using snails in other genera. If it's not using snails in other genera, then it is probably not using a mussel, which is in a completely different order.

Keep in mind, we are just talking about one species of fish- loving trematode (black-spot). Many more exist. Your question is right-on!!

Thanks Shawn, I learn more everyday.

I once had a lot of snails and mussels until a three year drought caused a sharp draw down which allowd raccons to get the mussels and emergent vegetation to almost die out. This year I could find no mussels and after inspecting plants all season I only found one tiny snail.

Once I thought snails would be a good thing because they ate and controlled algae and vegetation which I wanted to some extent and provided forgage. I guess I was lucky I never had any dieased fish because there is a lot of bird traffic from a nearby large lake.

I have only been able to find 1-3" redears in central illinois, I usually have to stock quite a few of them to get them established in stocked ponds.

If it's not a big pond, you could grow out enough RES in a tank first.