Bronze Corydoras Aeneus Fry Dying After 6 Weeks

[willemp]

I was lucky to buy a male and female cory. They have been spawning since I got them.

I had a fungus problem with the cory fry in the breeding tank and they all died.

I then noticed about 5 fry in the main tank (the eggs were not eaten). They were approximately 2 weeks old when I first saw them.

I just left them and they grew up nicely to about 1.5 to 1.8 cm.

Since week 6 they started dying. One after the other they disappeared. I saw one of the last two just lying on his side but not dead. I “buried” the fry and about two days later I saw the last one doing the same. He seemed healthy beforehand.

He was lying on his side at times, and it was not difficult catching him. I put him in the breeding tank and added some Methylene Blue (out of desperation as I really wanted to save him). I also got some API Furan-2 Anti-Bacterial medication.

That was 2 weeks ago and he is still alive, but he still behaves the same - sometimes lying on his side as if to die, but then swimming off, bumping into the glass, etc.

I do daily water changes and feed him the same the other catfish in the main tank receive – Nutrafin Max Bottom Feeder Sinking Food Tablets and TetraVeggie Algae Wafers. The main tank gets fed every other day.

The water readings in the main tank are:

Ammonia – 0
Nitrite – 0
Nitrate – 10
PH – 7.0
KH – 2
Temperature 26 C

I do weekly changes of 30 to 40L. The tank size is 140L and I have an Eheim Professional filter,

My main question is:

Why, if the fry grew up in the main tank for 6 to 7 weeks, do they start dying only then? I do appreciate that there is a big mortality rate. I would have expected them all to die very young because they did not get the right food etc, but they were getting nice and big and eating with the adults and other fish.

Moving the eggs to the breading tank doesn’t help as they start getting fungus after a few weeks (the last batch got fungus after 4 weeks) and even putting Methyl Blue in after I saw it, didn’t help.

The other fish in the tank are:
Zebra Danio
Rasboras
Rainbow Shark
Bristlenose catfish
Bronze Cory

None of the fish are aggressive and never bothered the fry.

I have lots of plants and hiding places for them.

I will appreciate any help on why they die at such an advanced age of development. I just doesn’t make sense to me.

Thanks

 

[KittyKat]

Rainbow sharks and zebra danios (the latter, in groups smaller than 6) are well known for being aggressive. Most fish will behave much better if people are around, so unless you are able to watch the fish all the time.. I would not discount that possibility. I can't easily see any other possibility.

There are ways to prevent fungus before it starts in fry tanks. For example, I have found that using almost anything which releases tannins into the water for softwater fish will at least help (such as new bogwood, oak leaves, Indian almond leaves), and it is well known that at least IAL have anti-fungal properties. Also it is possible to use a preventative "half-dose" of some medications (such as eSHa 2000). Regular water changes, where fish crap is removed from the bottom of the tank will also help in bare fry tanks.

I normally advise strongly against using methylene blue as it will kill filter bacteria. Although, it still works well for dips.

 

[Coryologist]

Fish can die for myriad reasons at any young age - and older fish, too - for that matter. If you unable to discern any physical signs or measure any water quality-issues, then I'm afraid that no one can tell you why your fish died. Anyone who purports to know why they died simply loves to hear themselves talk. Ignore them. lol.

This happens to anyone who breeds Corys, including the so-called, "experts." With experience comes acceptance of the fact that this happens and usually it's a mystery.

If spawning and raising Corys to adulthood were that easy - who wouldn't be doing it?

I know that these occurrences are extremely disheartening, but the secret to success is patience and perseverance.

Keep at it. - Frank

 

[Harlequins]

I agree with Frank ,its just what happens,i had a hard time trying to raise fry,kept dying like yours,then it went through a phase of lots surviving and now its back on a lull again,with only dozen a so still going from 100+ fry.I've done nothing different to what i normally do.

I just take it has it comes and hope it turns out well,although still sad to lose them,especially when they grow to a certain size & age and then sadly lose them...

Just all part of nature me thinks...

Good luck with future fry,dont give it,it is worth it in the end to see juvi cory flying around the tank

 

[willemp]

Thanks for the info.

Yes, its quite disheartening to see the little ones go, but I was just worried I was doing something wrong.

I seem to have saved the last one, as he is swimming around in the small tank and eating normally.

Next batch I'll try the fry tank again and hopefully I can contain the fungus.

Regards and happy "fishing"

Willem