First, you will want to limit your questions to the pertinent forum. Posting the same questions to mulitple forums tends to irritate people and reduce the chance you will get a reply.
There really is no fish that is perfect for cycling a tank. When you cycle a tank you are creating a bacteria colony that is essential for the water system. Adding living elements that produce ammonia triggers the cycle which begins with a huge spike in ammonia, then the ammonia is converted to nitrites, then nitrates. Damsels and some clowns (converted freshwater mollies too) are considered good for cycling tanks. Unfortunately, making an animal live through a cycle where the waste is so high is stressful, cruel and needless.
Since a fish has to swim, eat and breath all in the same environment, a water column with all the aforementioned waste is stressful and cruel. It would be like a human not flushing their toilet or taking out the garbage for a month; things would get pretty bad.
Stress can also lead to some diseases like fin rot and ich, and if your cycle fish contract these, you'll have to let your tank sit for nearly a month to clear out all of the parasites that cause stress induced diseases. So if your cycle takes a month, your fish catches ich and you have to let your tank sit for a month, it's going to be at least two months before you can really start to enjoy your tank.
You can throw a raw jumbo shrimp in and accomplish the same thing. Depending on your tank size, 1-3 shrimp should do it. Throw the shrimp in, let it start to decompose and you will have started the cycle (from the ammonia the rotting shrimp gives off). I removed my shrimp after three days in my QT tank and that's all it took.
You may want to do a search or look in the FAQ forum for more information on cycling. Welcome! Keep asking questions, this is a great forum!
