I aquired several goldfish recently and found they are quite entertaining. The only problem is they make noises throughout the night, it's okay though. I didn't have much luck teaching mine to fetch, hopefully you guys will.

I had to comment as the other reviews are painting a bad picture for goldfish. Common single tailed goldfish will grow to 12+ inches and live for 25 years or more if cared properly. They need an aquarium or pond with a minimum 40 US gallons with every additional goldfish needing 20 US gallons on top of the initial recommendation, to clarify 2 sarasa comets or commons would need 55 gallon minimum tank or pond. They are very messy fish by having an inefficient digestive system they should therefore have excellent filtration to account for this and I recommend double the amount of filtration to tank size, so if you have a 55gallon tank you will need a filtration system designed for a 110gallon tank.

Goldfish colouration changes with time the changes are slow and gradual so you may not notice but is not unknown for a pure black goldfish to colour morph to a red or even white colouration, most show less radical changes however.

Goldfish can be petted and contrary to popular belief they have a memory span of around 5 months so can be trained. You need to be extremely careful when petting they have a slime coat protecting them from disease (sounds revolting but you wouldn't know it was their unless someone told you as its very thinly spread) if you are rough during petting the slime coat will become damaged and they are very prone to illness. They can be hand fed and due to the long life span of goldfish and reasonable memory they will interact with you like a water-borne puppy.

They are easy to breed given the proper environment and with excess space for the fry accounted for, you can induce breeding by adding a heater and gradually raising the temperature over a period of a month. This make the fish believe they are in spring and summer is coming so will breed. The babies will predominantly have a dark colouration and those which do not are generally lost due to predation from their parents. It will take 8+ months before the babies attain their adult base colour.

I know you are thinking about the traditional fish bowl with 5L of water and a little goldfish which appears happy as it lives for a number of years and doesn't grow. They grow provided their environment allows, stopping this growth through inadequate conditions causes serious health issues for goldfish as their organs do not properly develop to their full potential size. The fish bowl is a poor design as the curvature of the glass distresses goldfish as everything is viewed out of focus and warped, some fish can live in goldfish bowls but goldfish ironically aren't one of them.

Fish can see out of their tanks and will interact with things they see, over time your goldfish will recognise you and even different clothing may cause your goldfish to exhibit different behaviour. Two of my goldfish are very big south park fans and will stay in the corner of the tank watching still whilst the show is on they then swim away for the adverts and return for the show when it continues. I am not sure what they associate with the show whether the music or the images make them react but it is a fun quirk to their personalities.

Goldfish are prevalent predators and will eat virtually anything I feed mine live foods as well as a staple flake diet. I also give them blanched fruit, vegetables and any creepy crawlies around the house or earthworms that I think they may like to nibble on.

Fancy goldfish are a whole different bucket of fish with individual types having quite exact environmental requirements, but I have whittered on for long enough. No goldfish should be kept in a tank smaller then 40 US gallons though, you may feel foolish for having a 4" goldfish in a large tank but it will grow rapidly and soon become very impressive

I simply adore my fish and would recommend them to anyone looking for a great, cheap and great looking pet.