I just read thyra's post. What i said there was true, i did a 25% water change and my fish were all at the top rapidly breathing. I didnt want them to suffer so i uthenized them.
That was a bit drastic action just because your fish were breathing rapidly. They were probably stressed from the water change or there may have been a difference in temperature in the water...or any number of reasons why your fish were at the surface breathing rapidly, NONE OF WHICH would be cause enough to euthanize them.
But there's on thing i just dont understand, my moms friend "inapproprietly" keeps fish like i did, and her's are still living to this day. She has 1 Silver tipped shark, 2 Cichlids, 1 Rainbow Shark, a Synodotis species all in a 55 gallon and shes had that for over 3 years. She has 4 Ryukin Goldfish in a tiny 5.5 gallon tank, had them for the longest time. The only difference between me and her is she kept her tank glass spotless, she didnt gravel vac sept every 6 months at a partial cleaning and she didnt do water changes, she just refilled the tanks water (had to be careful because the Silver Tipped shark would slap her tail and water get the lights wet and break them)
Why has her tanks been okay and all mine failed?
Some people get lucky.
I have a friend who has a fancy goldfish (about 5") and a common pleco (the "new" one she just got from her sister's 10 gallon tank is about 6"...her other one was almost 8" before it died) in a 28gal bowfront. The goldfish would be fine in that size tank...if she kept the water cool, but she keeps it at 78F, like a tropical tank. Her fish have been in that tank for at least two years and are "fine," except the fact that she had fancy guppies that were dropping like flies. She never does water changes and when she does clean the tank, it's a full strip-down and scrub.
I kept nine female bettas in an 18gal tall tank for almost a year when I first started and never lost one. I never did water changes, did the full strip-down clean, and was technically WAY overstocked. In fact, at one point I added a small trinidad pleco (not knowing better), but got rid of him because he fouled my filter with his poop. Then I got otos and never lost one.
The thing is, fish kept in less-than-ideal conditions don't live as long. Period. Most of the fish in your friend's tank won't live their full lives. Most of those fish live 5+ years in ideal conditions. I would be willing to bet that your friend's fish are stunted (at least the silvertip is...they are supposed to get 24" long).
Here is what I have learned about fishkeeping and hopefully you'll come to understand this as well:
Fish are living creatures that depend on us for their care, the same as a dog or horse. Just as you would not make a dog or horse live in too-small accommodations (like a tiny dog run or in a barn stall with never being turned out) and in their own feces, you should not make fish live in those conditions. We need to try to provide the best care and environment possible for the animals we care for. For fish, this means researching their natural habitat and mimicking those habitats to the best of our ability. Most of the fish commonly kept in aquaria come from rivers and streams where the water is clean with no ammonia build-up from waste and that allows them to swim freely and reach their maximum potential size. We should strive to keep our aquarium water clean with no ammonio build-up from waste (which is accomplished by cycling your tank and doing water changes to remove excess waste). We should also strive to provide at least the minimum space requirements needed by the fish we keep. This means having a tank large enough that the fish can reach their maximum potential size while in our care. We should also provide the fish with tankmates that are naturally compatible to avoid aggression and deaths that would not be found in the wild because those species would never be found mixed in the wild. This means having the appropriate numbers of fish to avoid aggression within a certain species, as well as not mixing fish that are completely incompatible just because we like the way they look.
We have a responsibility to the creatures we care for and honestly, I don't think you get that, Fishman.