Matt Clarke on the stunning Two-banded soapfish, Diploprion bifasciatum.
Common name: Two-banded soapfish, Barred soapfish, Yellow emperor
Scientific name: Diploprion bifasciatum Cuvier, 1828
Origin: Most commonly reported from Australia, but also found in other parts of the Indo-West Pacific from the Maldives, India and Papua New Guinea. Occurs as far north as southern Japan and as far south as Lord Howe Island in the Pacific off east Australia.
Size: Up to 25cm/10".
Diet: Stomach analyses have shown that D. bifasciatum feeds on fish and crustaceans such as crabs and shrimps.
Aquarium: Due to its size and diet this species is only suitable for a moderately large fish-only marine aquarium. According to Kuiter and Tonozuka's Guide to Indonesian Reef Fishes, this species has greatly protrusible jaws and can swallow surprisingly large fishes whole, so be careful what you mix it with.
It lives on reef faces, overhangs and rocky crevices on protected reefs, so provide plenty of shelter.
Like other soapfishes, Diploprion bifasciatum, can release a toxic secretion called grammistin through its skin as a defence mechanism. This protein is ichthyotoxic (it kills fish) and has been shown to be antibacterial. It's important to handle the species carefully and avoid keeping it in situations where it might consider releasing this secretion, such as alongside potentially aggressive fish.
Some fishkeepers have reported success in keeping several members of this species together in the same aquarium without aggression.
Notes: There are two geographic forms of D. bifasciatum. This is the most common one. The other form is predominantly black with a yellow anal fin, soft-rayed dorsal and caudal fin, and yellow margins on the pelvics. The latter fish occurs on the Great Barrier Reef and might have evolved different colours to allow it to mimic other species found in the area. The personifer-like Yellowtail angel, Chaetodontoplus meredithi, has been suggested as a possible mimic, but if it is, D. bifasciatum still has some evolving to do until it accurately mimics its pattern.
In Java, juveniles of D. bifasciatum are a different colour to those found elsewhere and are believed to be Batesian mimics of a poisonous fang blenny found in the area.
Availability: Although still not a commonly seen species, this is one of the more common soapfishes seen in the shops. We photographed this one on sale at The Water Zoo Peterborough.
This article was first published in the March 2008 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.