3 Questions - Goldfish fry & newt tadpoles in same tank, when to release them & water changes?

by Deb
(England)

Hello!, and thank you for any advice you can give me.
It’s been really exciting and fascinating to try to raise goldfish fry we love watching them developing everyday.

Are goldfish fry safe in the same tank as newt tadpoles? When I removed blanket weed from our pond I put it in buckets for a day or 2 so I can return anything living back to the pond. I found what I thought were all fish fry. This is my first time trying to raise fry from the pond. As they developed it turns out we now have 6 small newt tadpoles and only 3 free swimming goldfish fry. The newts seem to stay on one side of the tank and the fish on the other. I don’t want the newts to grow larger or faster than the fry & eat them. I realize I could just get another small tank, but it all gets costly and the water conditioning takes a bit of time. Of course I will if it keeps everyone safe.

I keep reading people are doing 50% water changes every day or so, is this really necessary? I use test strips to check water quality & clean the bottom of the tank often, with a turkey baster. I have filters, an air stone and a water plant, the water is clear. Everyone seems ok. I do not use a heater.

When do you recommend I safely release the newts & goldfish back into the pond with the other large goldfish, I don’t want them to be eaten if possible.

I hope I don’t have too many questions, I can find plenty of information to read about either newt tadpoles alone or goldfish fry alone but not together in the same tank.

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Grant's Reply


Hi Deb

Both Goldfish and newts will eat each other given the chance.

Looking at the size of the Goldfish fry, they would need to get quite a lot larger to pose a threat to the newt tadpoles.

Size for size, newt tadpoles have far bigger mouths than Goldfish fry as their diet is other living animals such as daphnia and worms, so I suspect it is your Goldfish fry that are in danger from being eaten.

The frequency of water changes is entirely dependent on how long it takes for the water quality in an aquarium to drop.

You are doing exactly what you should do, which is test the water. That tells you exactly when the water quality is low, and a water change is required. Newts and Goldfish both prefer the same water conditions, with a pH of around 7.0, and nitrates less than 30 ppm.

I would suggest using a test kit that has test tubes and indicator chemicals in it as the test strips are notoriously inaccurate.

With the setup you have, and the small number of small inhabitants, water changes should be required very infrequently at this stage, unless you are over-feeding.

As for releasing the newts and fry back into the pond, the Goldfish fry should be about 1/3rd the length of the largest fish.

This may seem quite large as at that size they won't fit in the mouth of a parent, but they will still be chased by the bigger fish until they get accustomed to their presence and not consider them food.

The other consideration is food, as the biggest fish dominate the feeding frenzy and the smaller fish are left the scraps.

And for the newts, they must not be able to fit into the mouth of the largest Goldfish. The size of the eye will give an indication of how wide a Goldfish can open its mouth, so the newt has to be a lot bigger than that.

Depending on newt species, some are cannibalistic, so the newts may be in more danger from the parents than the Goldfish. They should at least be past the tadpole stage before being put into the pond.