First, you can predict which fish may have been treated in that fashion if you know the animal's natural history. Certain fish are more prone to gas bladder over-inflation when brought from depth than others. Some fish are not collected in shallow water, so may almost always be "needled". So: pyramid butterflyfish are almost always needled, while green chromis from shallow water would never be. What species are you talking about, and where was it collected?
The most commonly seen symptom is incomplete de-pressurizing of the gas bladder - a Genicanthus angel that bobs head down for example. Secondly seen symptom is a red lesion on one side of the fish in the location of the gas bladder. Thirdly, TWO lesions, one on each side (meaning the collector ran the needle all the way through the fish). Worse yet, a single red lesion below the location of the gas bladder (meaning the collector ran the needle into the fish's viscera). Finally, unsubstantiated, but I wonder sometimes when you see a fish with ascites (fluid build-up in the gut) that this isn't caused by needling...with the fish's kidney riding right above the gas bladder, you have to wonder if damage there doesn't cause some of the ascites we see in deepwater fishes).
Healing is almost always a "wait and see" thing, although oral antibiotics might help.
Jay Hemdal
