Gardneri killifish fry emergency!!

[Lloydlost]

I've been raising a batch of 40+ gardneri fry in bucket outside.  Today I noticed them gasping for air and on closer inspection I saw most of the fry that were 1inch and above were either  struggling or already dead. The water was smelling really bad as well. 

The bucket had no air,  it was outside,  and had a plenty of guppy grass. Over the past 11 days ive been away and my mom has been feeding them,  also the top was covered with duckweed. 

I know it's a terrible situation but any insights to save the rest of the fry would be helpful

[Andy's Fish Den]

I would do a 50% water change, remove some duckweed and if you can, add an airstone. If I had to guess, since some else was feeding, they overfed., with all the duckweed, there may not be enough gas exchange at water surface.

[Lloydlost]

Thankyou so much for replying I did all the above,,,is there a reason why the older fry died and not the younger ones? 

[Andy's Fish Den]

1 hour ago, Lloydlost said:

Thankyou so much for replying I did all the above,,,is there a reason why the older fry died and not the younger ones? 

No I don't know that. It could be something along the lines that the younger ones were able to acclimate easier to poorer water conditions as the water parameters changed.

[Paul_Obermiller]

Or that they didn't need as much oxygen as the bigger ones.