Growth of the dorsal on heniochus

[SDguy]

OK, I'll admit, this is going to be a weird post. But I have always wondered about this, and now that I have one, I figured I'd ask.

How exactly does the dorsal spine/pennant grow on a heniochus.

Fresh imports with large pennants have an actual dorsal spine running the entire length, and a "thick" or "tall" section of tissue attached to it. I've seen the same thing in specimens at LARGE public aquarium displays.

In home aquaria, they seem to grow a lot of flimsy, rippling-in-the-water-column tissue, but very little actual dorsal spine. And the tissue is thin and stringy, not "tall".

So what's going on?

 

[tcmfish]

Tough question to answer and who knows the real answer, but maybe the dorsal spine takes longer to grow and the specimens you are seeing in large aquariums or fresh from the wild may be quite old and big compared to the smaller fish usually housed in our aquariums.

 

[SDguy]

My other thought was space. Perhaps with VERY long lengths of room for the fish to swim in, there is not as much back and forth swimming action, so the new growth doesn't snap back and forth as much. Does that even make sense? :lol:

 

[pab2005]

Maybe its depth of water. In Killer Whales in captivity the usual upright dorsal fin of the male flops over in captivity and I was told that the lack of depth and water pressure was the cause. I believe it was due to the development of the cartilidge in the fin. Maybe something similar.

I've just got 2 Heniochus with lovely profile and upright dorsal fins

 

[SDguy]

How large is your tank? I'll be interested to see what happens to those fins. IME all the long term heni's I've seen in home captivity have small dorsals....