Threadfin Butterflyfish

So far I've posted two clips of fish that look like butterflyfish so this time I'm posting the real thing. This is
Chaetodon auriga, the Threadfin Butterflyfish, so named for that very thin "thread" coming off its dorsal fin.

They come in pairs

Its not unusual to see pairs of fish swimming on the reef - in this case what I thought at first glance to be two damselfish turned out to be a pair of two-barred rabbitfish. Its interesting how they stayed together, despite being pursued by a giant potential predator (me). Not the first time that I saw paired fish moving together rather than splitting off in different directions.

Pairing behavior is better studied in some species of damselfish, where monogamous pairs of individuals will stay in close proximity on the reef, maintaining a territory and reacting antagonistically to any intruding fish from the same species. The pair of Blackback Butterflyfish (Chaetodon melannotus) I observed below seemed to be a pair, but later I saw a third Blackback come and join them without any conflict.