The pattern of distinctive white stripes on clownfish depends on the species of sea anemone in which the young fish develop — and could be a response to the conditions offered by a specific anemone.
Vincent Laudet at the Okinawa Institute of Science and Technology in Japan and his colleagues studied orange clownfish (Amphiprion percula) in Kimbe Bay, Papua New Guinea. They found that young fish residing in Stichodactyla gigantea anemones developed more white bars, and got them earlier, than did those living in Heteractis magnifica.
The researchers exposed clownfish larvae to varying concentrations of thyroid hormone in the laboratory and found that the white bars appeared soonest in fish that had received the highest dose. Analysis of samples of clownfish found that those living in S. gigantea had higher levels of thyroid hormone than did those living in H. magnifica, which the authors say explains why the white bars developed faster in those fish. A genetic analysis of the fish found an over-expression of duox, a gene important in thyroid hormone production, in those dwelling in S. gigantea.