My goldfish is dying

Question

I have had 2 goldfish for 2 years in my aquarium. This one was good last night. I don't know what happened today it is somehow floating on side with little movement, like sleeping. I put it outside of aquarium with filtered water now. When I bring my finger near it, it moves a bit, but very slowly, which is sad.

I didn't change the aquarium water for a while (maybe a year - my impression is they enjoy dirtier water, like pods - as you see it was full of their poop). But if it was for the water, the other one should have got sick as well.

What happened? Is she dying?

UPDATE 1 (1st week):

After a few hours of putting it separately in that bowl with fresh filtered water and a bit higher temperature, she got better now and swims. But the cause is still unknown to me. I changed the aquarium water and will get them back to it after a few days.

UPDATE 2 (2nd week):

After a week and a few days back in aquarium, I see the same thing happening. I got her back to a bowl now. I see her left side is always up when tilted (like this photo above) and when she swims, she gets upside down and has no balance. Is it swim bladder? I gave her pea pieces, but how much should I give her? And does it cure her?

UPDATE 3:

Unfortunately she died, which is incredibly sad. I performed an autopsy to realize what was wrong. Here are two photos (viewer discretion advised). What was wrong?

Answer 1

I worked at PetSmart for a little bit and what I found out (or really, what co-workers told me) is that goldfish don’t have stomachs so they can’t filter food. This causes them to poop a lot which produces ammonia and then kills them. So it’s essential that they have a filter.

It sounds like your aquarium may already have a filter. So I’m not sure what really could be “killing” it. Maybe another fish hurt him or something else could be going on!

If you keep him separated, make sure you maintain filtered water and have an appropriate temperature.

Best of luck!!

Answer 2

Bro... You didn't change the water for a YEAR? Plus the tank is too small. What happens is the poop they produce creates levels of different stuff in the water, like ammonia and nitrogen, and too much of the latter will cause permanent brain damage. The other also has negative effects and this can stunt growth. Having a small tank also stunts growth. Your fish won't live long, that's inevitable now because the damage has been done.

It sounds as though she was suffering more due to buoyancy problem in her bladder. Which can be remedied with either fish medications or with natural treatment, keep the air oxygenated well with an air pump and keep the water filtered so that she will not drown or suffer further damage. Feed her with boiled/deshelled/mashed pea (one or two, this acts as a laxative and clears out her system, so keep the water changes going). She should recover from this, but they will both die soon if you leave them in that tank with that water. You should do 10% water changes every week/week and a half and filter the water. With an air pump if possible.

They preferably need at least 20 gallon tank, maybe a 15 would work, but a 20 would definitely be better for them if you can afford it. Hope things improve.