Lonely Fish

[KnightReefer]

My yellow tang of a little over 2 months died over the weekend unexpectedly. He was eating/grazing and swimming normally then over the course of a couple days became less active and hid most of the time. He was in my 90 gallon tank. My water parameters test fine and the only other tankmate besides a few corals and snails is a skunk cleaner shrimp. It was brought to my attention that sometimes fish, especially those that generally school or shoal in the ocean, need some companionship from other fish in order to feel safe and secure in a captive system.

Any thoughts on this theory?