My understanding is we haven't really studied which (if any) tangs are venomous, but they all might be (though if they are, it would be a very mild toxin by all accounts I've read):
"As described and documented by
Halstead (1970,
1988),
Smith and Wheeler (2006), and the current study, the venomous dorsal spines in jacks (
Fig. 2B), gurnard perches, rabbitfishes (
Smith and Wheeler 2006: fig. 3G), scats, most scorpionfishes, most stonefishes (
Smith and Wheeler 2006: fig. 3E), tangs, and weeverfishes have converged on an anatomy where there are multiple anterolateral grooves on each fin spine that contain yellow to orange venomous tissue."*
"It is believed that some species of
Acanthurus have venom glands while others do not."**
"The genera
Acanthurus, Ctenochaetus, Paracanthurus and
Zebrasoma have sharp, movable blades that are embedded in a skin sheath at the base of the tail when in the resting position (Fig. 4.24). If the fish is under threat, these blades are erected outwards from the posteriorly located articulation. Thus surgeonfishes can use this blade to inflict deep, often fatal gashes by beating their tail when swimming past an attacking fish.
The integument that covers the blade is very thin and poorly developed in some acanthurids. In some of the larger species, however, it is quite thick and equipped with a secretory function. However, it is not clear whether these secretions are toxic."***
*Source:
Venom and its associated delivery systems have evolved in numerous animal groups ranging from jellyfishes to spiders, lizards, shrews, and the male platypu
academic.oup.com
**Source:
Acanthurus chirurgus This pancake-shaped reef fish is blue-gray to brown colored with thin, dark bars down its sides. It is sometimes offered as a fresh catch locally, but can cause ciguatera poisoning in humans. Handle with care during an encounter because of the sharp spines hidden in the c
www.floridamuseum.ufl.edu
***Source:
