Cory fry swimming too much??


New Member
Dec 16, 2018
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My corys had 100+ eggs and about 60+ hatched and now I have probably 40-50 fry that are a few weeks old (2-3 weeks), they are swimming all over the breeder box and I noticed today they are basically all swimming up the sides of the breeder box.. should I be concerned? Are they not getting to oxygen enough, is the water too warm or cold? (It’s sitting at 79 right now), are they hungry? (Scared to overfeed) or are they just swimming around because they can? Help!! I didn’t breed the Cory fish, nor have I ever had eggs and now I’m a mama to 40+ cory fry :)


Fish Expert
Feb 25, 2009
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Swimming actively is normal for cory fry, up to a point anyway. But the temperature is warm for cories, though some species will manage but others would prefer it closer to low to mid-70's. Warmer water does contain less oxygen of course, and fry are more delicate when it comes to such things. I'm not saying there is a crucial issue now, but the temp should be a tad lower.

I assume this box is in the main tank. The box itself is certainly going to stress the cories. They need sand below them, and cover available. The sooner you can get them into a small tank (if too small for the main tank), or released into the main tank, the better. However, feeding them in the main tank can be challenging, so a small (10 gallon) tank would be best.

Dried leaves provide infusoria, and the fry will develop faster with leaves in their tank. Oak, maple, beech are safe (pick them up from the ground as dead leaves and rinse off). A few of these in the box would help. You also need to provide food. I use dried leaves and add a couple shrimp pellets. Fry foods are an option, though I have never used them.


Fish Guru
Jan 26, 2008
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Perth, WA
Hi and welcome to the forum :)

Whilst adult Corydoras prefer cooler water, I would not lower the temperature just yet because the fry will not be strong enough for a major temperature change. However, when they are a couple of months old you should reduce the temperature.

As Byron said, try to move them into a spare tank where they have more room to move. If you don't have an aquarium to put them in, you can use a large plastic storage container. Make sure it is clean and hasn't been used for any chemicals or anything nasty, then set it up with a thin layer of sand, a heater, filter, and some plants (real or plastic) for cover. Feed them a varied diet and do regular water changes and in a few months time they will be big enough to go back in with their parents.

There's more information about rearing fish and growing fish food at the following link. It's pretty long and usually easier to read if you print it out and read it in bed to help you fall asleep.