Can Worms Survive In A Fish Tank?

“I was curious if red wigglers could survive under the gravel of a fish tank. We have a 120 gallon freshwater tank and, yup, I dropped a worm or two in to see what the fish would do. No surprise they tried to eat ’em, but the worms were too big and got away and wiggled under the gravel.

I have since dropped in a few, maybe a couple per month, and those also make it to the bottom and disappear (we have small fish, but lots of them.) I thought they would just die and disintegrate, but when cleaning the tank and suctioning the gravel the other day, there were several intact worms that got sucked up from the same corner of the tank. I could not tell if they were alive as they went through the hose, but it made me think that maybe there were still alive since they were still whole.

Do you think they could have been alive under the gravel?? We do have quite a lot of aeration in the tank. I also noticed that the water in the tank has been very clear and I was wondering if you think the worms could be credited with that also. Could all the good enzymes, etc. that they produce be keeping the water clear, or is it just hubby’s diligence in frequent water changes?

Most importantly, do you think I could be doing any harm to the tank if I continue to drop a worm in now and then? Thanks for your info!!” ~ Bobbie McCoid

Hi Bobbie,

Worms breathe through their skin, which needs to be moist.

The worms breathe by oxygen dissolving in the moist skin which then diffuses through into the bloodstream.

In a water tank, the water should be pretty well dissolved with oxygen since most aquariums will have an oxygen pump to provide oxygen for the fish. Some oxygen pumps will also have oxygen pumping through the ground of the aquarium through the gravel.

This makes the area beneath the gravel a well oxygenated place, and worms can survive in these conditions. As long as there is oxygen diffusing into their blood stream, it doesn’t matter that they are in water.

In terms of the cleanliness of the fish tank, it probably is due to a large part on your husbands effort to clean the tank! However it does make sense for a cleaner tank with worms crawling about, since algae grows on the gravel, which then spreads across the whole aquarium.

The worms may be controlling this population. But I doubt that a few worms really do make a big difference though.

Is there any harm to the aquarium and the fish?

I highly doubt that there would be.

If the worms are alive, they will be under the gravel to escape from the light and will probably help with controlling the algae growth (but this is untested so don’t quote me on this one!) If they do die they will slowly disintegrate into smaller pieces which I am sure your fish will find nutritious.

The only thing I am concerned of is the wormcast produced. Although this is dense and will probably sink and stay under the gravel, it may soon become unsightly. But since your husband keeps the aquarium clean, this shouldn’t be a big problem for you!

Now please note that the worms I am talking about here are earthworms.

In a fish tank there are different species of worms that WILL cause trouble.

Take the planaria for example, because of their high rates of growth, they start to compete for food with the fish affecting their normal growth. Earthworms on the other hand do not replicate and grow quickly for this problem to occur.

If your worm adventure doesn’t seem to be harming your fish, and as the aquarium is well oxygenated, I don’t see the problem of keeping some there!

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