I've noticed that there is a hole on the front tip of the "dorsal fin" of the CRJ-1000. I've been thinking that it would be logical if that's the intake for its APU unit. But I'm not really sure.
It is the Ram Air Inlet Duct for the cabin air system. It normally acts as cooling air for the packs but can also be used as an alternate vent source in an emergency.
The cooling efficiency of each air conditioning pack is enhanced by ram air cooling via a heat exchanger. Ram air enters through an inlet at the abse of the vertical stabilizer and passes through the pack heat exchangers and then exits overboard. In case of failure of both packs, ram air can be used as the sole source of ventilation. This is accomplished by opening the ram-air valve via the RAM AIR switch. Ram air then enters the occupied areas through the normal vents.