What is "very common" depends on where you are. According to Randall, the commonest surgeonfish in most places where it occurs is the Striated Bristletooth (Ctenochaetus striatus), but it doesn't have any white on it. The Brown Surgeonfish aka Dusky Surgeonfish aka Brown Tang (Acanthurus nigrofuscus) is also very common in some locations, but again doesn't have any white on it.
I don’t have a photo as I don’t have an underwater camera. Sorry something I should have mentioned before the fish described in my post were quite small so presumably juveniles. The larger tangs I saw didn’t have the white spot on the tail. They were definitely not Naso lituratus, as I saw most of this fish from less than 50cm away.What is "very common" depends on where you are. According to Randall, the commonest surgeonfish in most places where it occurs is the Striated Bristletooth (Ctenochaetus striatus), but it doesn't have any white on it. The Brown Surgeonfish aka Dusky Surgeonfish aka Brown Tang (Acanthurus nigrofuscus) is also very common in some locations, but again doesn't have any white on it.
No Surgeonfish has a white spot on the tail. Many have a white bar at the base of the tail, and Acanthurus thompsoni has a white tail in some locations, but most of these have a blue or grey background colour. However, acanthurids have the ability to quickly change their colours and can look very different, and this can effect the edges of things like bars to make them look more ragged (and possibly 'spot'-like). Usually they are darkening from pale greys and blues to almost completely black. I suspect the fish you've been watching have ben doing something like that.
Also possible is the Orangespine Unicornfish (Naso lituratus) which has a white spot between the orange peduncular spines. I've seen them in large schools where, from a distance of 10 metres, the orange spines are not visible, but the white spot on the peduncle is quite distinctive. Their background colour is usually grey but they can get quite dark too.
A photo of your fish would be helpful.
Hix
It's always great to see mantids in my backyard. Such cool insects.
Birds
All seen wild at Healesville Sanctuary today
There are wombats at Healesville? I didn't know that. Whereabouts would they be seen, and what time of day was this?All seen wild at Healesville Sanctuary today
MAMMALS
13 - Common Wombat (Vombatus ursinus)
This one was walking on the path between the entrance and the information booth, opposite the emus, at about 3:15 PM. There are quite a few that live around the area, but you rarely see them as they're not too active in the day. There are one or two burrows in staff areas and there's one near the bridge between the Kangaroo Island Kangaroos and the Wildlife Hospital. I volunteer weekly there though and have seen maybe three wombats in four years. If you happen to be in the area and do really want to see a wombat, there's much better and easier places to go spotlighting for them.
A great day of birding day today, mostly along Lake Michigan:
I looked back at my photos and it turns out this is actually:
