The fish did not seem too concerned at my presence, or perhaps it was taking advantage of my being there. It was rooting about in the cave rubble, using its sensitive barbels to detect prey under the debris and sand. As I watched it would slowly sweep over the rubble, then suddenly and vigorously rummage about in a cloud of sand. I could not see if the fish was having any success, but it was interesting to watch.
So often fish and other marine creatures will modify their behavior when a diver is present. It is always interesting when you run across something continues on despite being watched. It is worth a few minutes of air to sit and observe, sit and learn.