Fautin and Allen (1992) did suggest that the formation of the bubbles was somehow elicited by the presence of anemonefishes, and that adding a suitable anemonefish could make a bubble-less BTA become a bubble-covered BTA. However, this certainly isn't always the case, as I've seen lots of contradictory evidence in aquariums and while diving, too. Delbeek & Sprung (1997) instead suggested that the presence or absence of bubbles has do with lighting and that the bubbles disappear and the tentacles get longer and thinner under lower light, or that it may have something to do with an anemone being hungry. While I agree that BTAs kept under intense lighting in aquariums do seem to be more likely to keep their bubbles, or to develop them where there were none before, again, I've seen otherwise at times.