Well, I saw the photos here of a member with a longhorn cow in their reef tank. As luck would have it, I spotted a really nice 1 1/2 inch one at my lfs. It circled the tank with horns protruding from the water's surface, seemed to make eye contact, ate readily... so I did what I usually chastize other for doing -bought a fish as an impulse buy.
I moved it from my 29 gallon quarantine tank to the reef last week and so far, so good. It spends most of its time near the surface and hours of observation haven't shown one instance of nibbling. I still have an empty quarantine tank to move him to if there is a problem, but I feel pretty confident about this working out. It's the most entertaining fish I've possibly ever owned. It eats from my hand, has his version of "Jaws" where he circles with both horns out of the water. I'll be happy to house this guy as long as it lives and highly suggest them as a specimen fish. As for a reef inhabitant; that's an ongoing study, but no coral or polyp damage so far.

Russy,

Very cool! I love how they look.

If indeed it reaches over a foot in length, I'd have no problem eventually getting a 125 or 180 for this guy. Not only are they really cool-looking, but the behavior is like that of a tame trigger; only you'd have a much broader selection of tankmates. That'll be a ways down the road though, it's pretty tiny.

Are cowfish related to boxfish and puffers?

They are boxfish (family Ostraciidae), but in they are in a different family than puffers (family Tetraodontidae). They have a hard "shell" that covers everything but their "lips" and caudal peduncle/tailfin. Most have poisonous flesh and can release toxins into the water if badly stressed.

Ah okay. A friend of mine had a little boxfish and it behaved just like you are talking about. Great critter. It died, however, and released the toxin you mentioned, wiping out his nano. Are they generally easy to keep?

This is only my second one, my first was some 15 years ago. That one didn't live long, but ignorance is bliss -it died with no ill effects to the tank.
My understanding is that they can be slow to feed, once eating, they are quite hardy. This one ate from my hand by the third day. I think they are more sensitive to water quality than some puffers, but I stay on top of my tanks pretty well and have good filtration systems. That is to say, the filter systems I run these days blow away the undergravel filer and AquaClear 2000 combos I used forever. I really like the blue Indo-Pacific spotted boxfish (male shown here)
http://i18.tinypic.com/54ap6px.jpg
and would like to try my hand with those down the road. As well as pipefish, nautilus, cuttles, octopi, and a handfull of other "dreamfish/mollusks." I'm about to have an empty, mature 55 and am really struggling with inhabitant choices.

Good luck on the Long horn. I have had one in a reef tank. He ate good, was really happy go lucky use to play like a dog with me. Spit water at me when i would hold food over the tank. Around a month later he was just going nuts on my Devils hand coral. I don't know why the snap but he did. I have also heard they like sponges. I hope he works out. Just remember there are alot of crazy fish out there that are not reef safe, that end up working in a reef. Alot has to do with the hobbyist and the fish attitude. On that note good luck and i wish along time with the longhorn.

Nate

The colors on that thing are awesome!