Heniochus diphreutes vs. acuminatus

[Anonymous]

I am often asked how to tell the difference between these two species of very closely related fish. The difference is an important one, because the two species reportedly have different tendencies to snack on corals.

There are several ways to distinguish the two species apart, including the position of the band at the tip of the anal fin and the shape of the breast, but I find these to be problematic (fin tips are often ripped) and/or difficult to readily distinguish. Variation occurs in individual fish making these traits hard to ascertain, and juveniles tend to change shape as they age. I find the easiest way to distinguish these fish is in the shape and size of the snout.

H. acuminatus has a longer mouth, with a greater distance between the tip of the mouth and the eyeball. Note the ridge or lip on the upper side of the mouth in H. acuminatus. (see below)

H. diphreutes, in contrast, has a much smaller and shorter mouth. The distance between the tip of the mouth and the eyeball is relatively shorter. (see second picture below)

The general consensus seems to be that H. acuminatus is NOT reef safe, and that H. diphreutes is reef safe. I am skeptical that IDing of these fish to the species level is done with any degree of certainty when hobbyists report their findings with these fish. I'd be curious to hear anybody's experiences with these fish while keeping them with coral, and ideally a photo of the fish.

 

[tdwyatt]

I havenot been online in a while, evidently neither has this topic, but I need to kmow as one is a planktonovore (H. diphreutes) and the other is a corallivore ( H. acuminatus), ever some dispute this!! In honor of my birthday, I intend to buy three Heniochus diphrates for my big (as opposed to the species RBRA tank) reef tank, but everywhere I have looked, the powers-that-be say they ( H. diphrates and H. acuminatus) are very similar and differ only in the number of rays on the anal and dorsal fins and the shape of their mouths and that their brests differ (with H. difreutes being more rounded); there are a few other differences that are difficult to judge at the LFS ( like overal size and not from Hawaii). Does anybody with some credibility have any clear-cut differences between these two species?