She was struggling to swim, sinking and started turning on her side. We rushed out and bought cambomba, eledora densa, and some marbles as we thought she might lay the eggs...
Current was overpowering her from filter so I moved her to bigger tank thinking she might just be tired.
Alas in the morning she was dead.
All others are okay.. not sure what caused it. She had been swallon for quite a while now, I did a little cutting on the body and saw some white little balls which I assume are the eggs.. and being white im assuming maybe they went bad?
If all water parameters are as they should be (ammonia 0, nitrite 0, nitrates under 40) then it sounds like she was egg bound. The colour of the eggs isn't really relevant as egg laying fish's eggs are not fertilised until after they have been laid. Determining fertility by colour can't be done until the males have made an attempt at fertilisation once the eggs are out of the fish and in the tank. Sorry you lost her
Zebra Danio females are generally larger and more rounded than males, even when not full of eggs. Egg laying fish don't become pregnant. Eggs mature in the female during which time she will become more rounded than usual. When the eggs are mature enough to be fertilised, they are released into the tank and then the male fertilises them. Danios tend to spawn very frequently, usually first thing in the morning. It won't do them any harm
If you keep an eye out when you're doing a gravel vac or when you're cleaning out your filter you're likely to spot the odd danio fry now and again without having to resort to breeding hundreds of them in a seperate tank. They look a bit like half an eyelash. I managed to raise a couple of danio fry last year doing this and then sticking them in a spawning net within the big tank.
There aren't that many reasons. The main reason for female Danios hanging on to eggs is simply a lack of males. Danio spawning is quite vigorous (almost looks aggressive) and that stimulates egg release.
She may not have been egg-bound, just quite likely given the info you supplied. If there were any other symptoms beyond swollen abdomen and lethargy it may have been a bacterial infection or just plain old age. Was there any sign of white or clear poo, heavy breathing, redness anywhere at all on the fish? Were any of here scales lifting (so she looked like a pinecone)? Was there swelling anywhere other than the abdominal area?
Oh dear. Found another Rose Danio dead this evening when I got. Showing 0/0/30 so I did a 50% water change to be safe. Had a swollen stomach like the other, but this one only started to swell since the other died.
None of the fish are showing any signs of distress, all feeding okay, none are gulping at the surface, even the oto's are fine?