Almost sounds like dropsy or TB beginings. Or, you could be feeding it too much and the water quality has gotten bad from it. Uneaten food and fish poop creates ammonia. When your tank cycles it is supposed to remove the ammonia. If you are feeding to much the uneaten food and fish poop overload the "bio-filter" and the "system" crashes. If the water quality is bad (meaning too much ammonia in this case) the fish stresses because of the toxicity. It is unhealthy and the fish is suseptible to disease and gets poisoned. Is this a new fish? (under 6 months) and are you new to fish keeping?

Thanks for your reply. Yes I am new to fishkeeping. I don't know how old my goldfish is as he was given to me by a friend who moved abroad. I think he must be at least a year or two old as he's pretty large.

He was very ill again today and I noticed more white spots on his tail. Also one can now see his veins clearly in his tail and his fins are very red neither of which was evident before! If anyone can give me an idea of what ails my fish and what I can do to help him get better, it will be very appreciated. I've become quite attached to him.

I've taken him out of the aquarium and put him in a bucket with fresh water for the night. Hopefully he'll survive. Tomorrow my OH and I will go to the aquarium shop with a sample of our aquarium water and hopefully get some advice.

I'll google dropsy and TB. Can I help my fish if either is the case?

OK, if you have only had the fish for 2 months and you are seeing red streaks or veins and spots are appearing on the tail then stop feeding. Your fish has ammonia poisoning. Do a huge water change, like 75% if possible. Use a good water conditioner like "Prime" and double the dose. You can do that with Prime. Also add some aquarium salt to the water, follow the directions on the box. Get a 2 part, reagent type, ammonia test kit. Reagent kits have a liquid chemical, in this case 2, that you add drops to a sample of aquarium water. They come with small vials to take samples with and usually have good directions that should be followed to the letter. I like Aquarium Pharmaceuticals or AP brand. They cost more initially then others but last long so you wont have to re-buy. I think your tank is still cycling, or if it did cycle, it has crashed. Feed fish sparingly only every 3 days until you resolve this situation.

Check ammonia level daily and change an appropriate amount of water to bring the level no higher then .25ppm until the tank does cycle. The Prime product removes chlorine as well as detoxifies ammonia. The spots on the tail are from ammonia burns and eventually will rot off the fins and tail if not addressed. Ammonia is very toxic to fish and even slight poisoning has long term effects. If you act in time your fish may survive if not to sick it may recover. I put a link on the bottom for a goldfish forum. I don't keep them anymore, but it is the same type of basic care. This site is more goldfish specific.

Here is a link that might be useful: Goldfish Paradise .com

Sorry about the bad experience. It sounds like it was ammonia poisonoing though. Usually when the signs of it appear, it is too late. If the fish pulls through, it usually has a shortened life span. It is hard to watch anything suffer. I would try a fishless cycle of the tank and filter next time. Then get the new fish. This way the tank wont become toxic and you really see first hand how it works. Once you do it, everything falls into place. Maybe you could call the new fish Felix? ;0) I never had trouble with fish as a kid, then when I moved to a different area, with a different water supply all hell broke loose. There are so many variables with water chemistry in town to town and even house to house that make the difference. I'll give a link about fishless cycling. All 5 articles are very useful. Or just go to cycling aquariums without any fish. Sorry again.

Here is a link that might be useful: biochemistry 101

my gold fish sits at the bottom and is unable to swim, please help me.