i just added some some fish to my 52 gallon, 2 of them are hidding them coming out, leave the light off for a while until they decide to come out. hes properbly shy. do you have any large aggressive fish in the tank?, if so then that might explain why. but usualy for the first week fish will be a little bit weary because its all new, after all if you were taken away from your friends and put into a tank with new tankmates wouldn't you be alittle affraid?
thats all i can realy say