Sick Tropical Goldfish

There isn't enough information to really come up with definitive plan. As you know, the 10G is a "little" overstocked so it was only a matter of time before something like this happened.

Since none of the other fish are affected, I will put ammonia/nitrite toxicity, pH crash, chlorine toxicity, and temperature fluctuations at the bottom of my list since it would probably stress the cardinals too. However, the only way to prove that current tank maintenance is adequate is to measure the water quality. With that said, you have to wonder what would affect a goldfish but not necessarily tropicals?

1. Goldfish have high oxygen demands which is one reason why they do not fair well at tropical temperatures although 25C (77F) is not that bad so I don't know about that. I know a lot of people who keep their goldfish tanks at 74/75F and I heat mine to 70F.

2. Parasites - One potential parasite could be gill flukes which are common in goldfish. See if you can get a look at the gills...they should be bright red with no spots or discoloration. I don't know if cardinals would be susceptible to this parasite. Also look for signs of white fuzz (fungus or columnaris bacteria). This can be really difficult to spot on some goldfish especially if the fish has and any silver/white coloration.

3. Internal parasites- These can affect a fish's apetite or the ability to absorb nutrients which potentially leads to an inability to control ballast. The fish begins listing to one side or the other and may eventually flip over.

It's probably not surprising that the biggest fish with the most space and filtration requirements is affected. A 6" goldfish is going to feel very crowded (i.e., stressed) in a 10G with 6 cardinals, an ancistrus, and another goldfish.

I am afraid that I cannot be of more help. Maybe some others will have more or better ideas. Can the fish be isolated so that it can be treated separately from the rest? Post when you have more information about the tank and good luck.

One more thing,goldfishes aren't tropical,that's explains why it is sick in the first place.

Is this gold fish floating more to the top? He may have bloat desease. Overfeeding and giving him dry foods instead of pre- wet foods do this. A thawed out frozen pea may save him. If this is the illness go to ..... http://www.geocities.com/Tokyo/4468/toc.html
good luck!

ps.....of course it may be his living conditions...that tanks way too small.

Once a fish is on its side, it's usually as good as dead. Muerto, I believe the Spanish word is.

The cause could be anything, but remember that warm water has less oxygen than cold, and goldfish like lots of oxygen. Is there any kind of aeration in this tank?

btw

just FYI, there's no such thing as Tropical Goldfish as goldfish are coldwater fish.

heres a good Koi/Goldfish symptoms and treatment page:

KoiVet

I've never been able to save a fish that exhibited the symptoms you've mentioned, but I am a big fan of extra aeration in tanks, especially if they are crowded. This might be something your friend can do easily and cheaply. Add a bubble wand or airstone powered by a simple air pump. This won't so much add oxygen to the water as increase surface agitation which will allow a freer gas exchange and give the GF a better chance...

HTH

Val

i agree. i have goldfish too and i give them aeration. though they're small, i find that goldfish has high oxygen consumption and some amount of aeration will definitely do them good.