Is it coming from its anus? If so, that is mucus feces. There are a number of causes for this - starvation, change in diet, bacterial disease and protozoan disease, and sometimes, no reason at all. However, since it is a new fish and you have no history with it, you need to suspect the worst. Did you buy the fish from a local pet store? If so, give them a call to let them know about it.
Jay