my freshwater cichlid actually would somtime choke on gravel too. it'd be in his mouth for days where he couldnt eat. i'd just net him out and use a tweezer to pull the rock out. the whole procudure took less than a minute. as long as u hv everything ready, its ok to take out the clownfish and get the food out. the best way to see if he is choking is to feed him. if he couldnt eat, do what i just describe. it wont hurt him one bit. just make sure u wear latex gloves when doing this.