Surgeonfish (Tangs):
Some information has been collected concerning the reproductive habits of marine surgeonfish...
Surgeonfish, along with rabbitfish they are gonochoristic (each fish is either male or female) rather than being hermaphrodites. There are few sexual differences, though in some Naso species the males are larger than females. For the others sexual dichromatism exists only during spawning.
Spawnings are tied to the lunar cycle, some surgeonfish will spawn on a new moon and others around the full moon. Many surgeonfish are group spawners, with fish coming together from around the reef late in the afternoon, forming a large aggregate. Others such as the Zebrasoma species, spawn in pairs.
The courtship consists of males searching out gravid females, and then changing colors and performing a shimmering movement to entice the female to spawn. The pair rises together toward the surface in an arc shaped path, simultaneously releasing their gametes into the open water at the apex of the arc. Males may spawn with several females in a single session, while sexually mature females spawn only about once a month.
After hatching, the pelagic larvae subsist on their egg yolk for a couple days and on day four start to feed on plankton. They then begin to develop into a specialized larva, becoming compressed and growing thorns on the dorsal and ventral fins. Their bodies are scaleless and transparent with a silver cast to the abdomen. This post larvae stage is called 'acronurus larva', and is distinct to the Acanthuridae. As they grow the body becomes oval, the spines on the caudal peduncle develop, and the thorns on the fins gradually disappear (except on some of the Naso species and on the Blue Tang Paracanthurus hepatus).
The planktonic stage will last about 10 weeks after which the young will then settle into a shallow reef. Though the behavior of the young will vary between species and with the availability of food, many are initially quite territorial. As they mature most species become less aggressive and begin to roam wide areas of the reef in large schools.
Some species of surgeonfish have spawned in public aquariums and there have been a few scattered reports of spawnings in aquariums, but regular spawnings and rearing of the young has not yet been reported.
found this here:
Breeding Marine (Saltwater) Fish 
breeding tangs 
jb
