No, unfortunately, there is no such thing as "dwarf" goldfish. The smallest you can possibly get is the extremely delicate bubble eyes at 6-8 inches size bracket. That's still too large for a 10g and goldfish are sociable by nature so keeping more than one is not an option either. A 10g works best as a hospital or quarantine tank though but that's all it can function for goldfish.
If space and money are not an issue, get a 40g as your minimum tank size if you want to keep fancy goldfish. Avoid pond types such as comets, shubs, wakins, hibunas and watonais as those are exceedingly large at 12-18 inches and need plenty of space more than a 40g can provide. It should however work for at least 3-4 fancy goldfish depending on the variant you are looking for. Make sure your filtration has a turnover rate at least 4 times and over the water volume of the tank. A canister filter may be your best bet but as long as your filtration albeit the turnover rate and filter media are adequate enough, they'll work just fine for a 40g.
Here are the size brackets for each variant available.
Ryukin: 8-10 inches
Oranda, Ranchu, Lionhead, Lionchus, Black Moors/Telescopes, Fantail: 10-12 inches
Pearlscales, shortbodied orandas, tosakins: 7-10 inches
Bubble eyes: 6-8 inches
Comets, Shubunkins, Hibuna, Jikin, Wakin, Watonai: 18 inches
If you opt to start with hardy ones, orandas, ryukins, fantails and lionheads will work just fine. Note that there are many lionheads often mislabeled as ranchus and vice versa. The same can be said between ryukins and fantails. I'd avoid the black moors for now if this is the first time you handle goldfish. They tend to be more prone to fluid buildup behind their eyes. Celestials, tosakins and bubble eyes should also be avoided as they are also delicate and are rather poor swimmers. Pearlscales cannot even compete equally with the likes of orandas and the rest except with varieties that can compete equally with them such as celestials.
I keep mostly orandas myself although I have ryukins, ranchus, lionhead and a few other varieties. My largest oranda is 10 inches in length. followed by a few others ranging from 3-8 inches. They are fed with homemade gel foods (mostly vegetable content, sardines, multivitamins, calcium, acidophilus, Knox gelatin and anything else), Hikari Lionhead (to promote wen growth for my orandas, ranchus and lionhead), Mazuri gel food (available at Goldfish Utopia website owned by Ed), aquarium plants, bloodworms, etc. They can take to shrimps, mussels and even daphnia. Just be sure your food sources are clean. Tubifex worms are best avoided regardless of the sources due to the possible myxobolus infection which can be rather troublesome to deal with.
Another primary concern with foods is the usage of freeze-dried stuffs, flakes and floating pellets. Those should absolutely be avoided for fancy goldfish with a very round body appearance as they tend to ingest air in the process as they eat those stuff making them more prone to buoyancy issues. This is why I preferred Hikari Lionhead over Hikari Oranda Gold as the former is a sinking type. Some goldfish though, due to genetics, may get floaty with Hikari Lionhead but it seldoms happens fortunately. You just need to check the labels and avoid floating ones and those with high starch and sugar content.
As for temperature, I keep mine steady at 74-76 degrees Fahrenheit. It sometimes goes up to 78 degrees but fancy goldfish are more tolerant to it than the pond types such as shubunkins. Fancy goldfish should not be technically considered as "coldwater" fish because they are not. They have lower tolerance to colder temperature than the pond types.
As for tankmates, the only tankmates I would ever consider are bristlenose plecos, dojo loaches, guppies (if big enough) and platies. They should work just fine along with some apple snails and nerite snails (not the horned species). Shrimps will not last with goldfish. Goldfish tend to look around for food and will not hesitate to gobble shrimps right into their mouths.
If you have any other questions, please let me know and I'll be more than happy to help.
Last edited by Lupin; 11-04-2009 at 12:17 AM..