Dead Cory

[LancsRick]

Just lost one of my Corydoras Longipinnis, found it floating upside down this morning, but when I went near it it swam off - has been upside down all day, so I added some API Melafix earlier (general bacteria treatment), but have just found it lying dead at the bottom of the tank. It looks fine, so not quite sure what caused it.

2 other Longipinnis, 3 Cory Schwartzi, 4 botia striata, 4 red honey gouramis and 18 cardinal tetras are all very happy in the tank, so not quite sure what the cause was, could it just be "one of those things"?

Tank has been stocked for 6 weeks now, fish loss has been:

1 Cory schwartzi - appeared to be a runt, never grew compared to the other 3, and was found dead after 3 weeks
1 cardinal - found dead floating one morning in the first week
MIA are 1 cory longipinnis and 1 cardinal tetra, not been seen for a couple of weeks now (I'm chalking these up to cannibalism, since I have seen ZERO remains).

Any observations or points for concern at all? Did a 25% water change about a week ago, but would be surprised if this was water related given that all other fish appear happy?

 

[darren636]

can you test for ammonia etc? How did you set up the tank and filter- cycle or fish in from the start?

 

[sparkyweasel]

Swimming upside-down can be caused by a build-up of gas affecting the fish's bouyancy. The gas can be caused by a blockage in the digestive tract, which causes food to decompose in the tract instead of passing through.Gas can also be caused by an infection. I believe a blockage is more common. It can also be a swim-bladder problem in those species which have a bladder.
Are your other fish OK? If it starts to spread you may need a broad-spectrum anti-bacterial medication, although the one you have used may have been enough to prevent any spread.
I would suggest keeping a close watch for the onset of similar symptoms in your other fish, and treat them immediately if symptoms appear. You could also prevent a spread to any other tanks you have by avoiding sharing nets, test equipment etc between tanks, or using a product such as Sterazin to clean them.
I am sure you realise there is an element of conjecture involved unless you can get a proper diagnosis from some-one who has examined the fish, but I hope this helps.