Yes, it is poisonous.
lack Spinefoot (Siganus spinnus Linnaeus)
Local Common Names : Happy Moments or Black Trevally
This species is included because the numerous spines on this fish are capable of inflicting painful stings; these endure for up to some hours and lend the ironic name of "Happy Moments". Special care is needed in handling this fish because the first spine of the dorsal fin lies close to the back, and is directed forward. Although a minor pri_ck results in some discomfort, the venom injected by a deep puncture leads to immediate and intense pain. The intensity of the pain may be out of all proportion to the size of the wound, which should be immersed in hot water as soon as possible and medical help obtained as soon as possible.
The fish grows to 350mm (14 inches) and is usually brown or olive in colour with a small mouth but is never the less hooked quite easily. If caught it is more preferable to cut the fish off rather than risk bringing the fish into the boat or on to land risking being stung.
The species is common on reefs, and in coastal waters, estuaries and rivers in the region.