RTN & STN

[treesprite]

Could someone please explain these to me, like how does each one start, what it looks like, what might cause it, and what to do if it's seen on a coral (& prognosis)? I am not finding specific enough information, most especially on STN.

Thanks

Edited November 22, 2007 by treesprite

[txaggies07]

Could someone please explain these to me, like how does each one start, what it looks like, what might cause it, and what to do if it's seen on a coral (& prognosis)? I am not finding specific enough information, most especially on STN.

Thanks

 

Good question. Hopefully someone smarter than me responds.

[lanman]

Could someone please explain these to me, like how does each one start, what it looks like, what might cause it, and what to do if it's seen on a coral (& prognosis)? I am not finding specific enough information, most especially on STN.

Thanks

 

I've researched it as well - there isn't much good information. Nobody has a clue what causes it, other than 'stress'. I've only seen RTN twice - except maybe on tiny frags which are there one day and gone the next. One was a LARGE piece of staghorn. It started at the base - the skin/corallites started turning mushy - and it worked its way up the stem, and started spreading out. Within a few hours, it had covered about 6 inches. At that point, I decided I needed to do something; I pulled it out and cut it up. It started out as a well-branched coral about 10" from side to side, and maybe 8" tall. I cut big frags from it, and separated them out in the tank. Only one 6" section lived. The RTN continued up all of the other branches; killing them within 6-8 hours of onset. The second was a 5" diameter monti cap. It started from a little point where a mushroom touched it. I managed to get a couple of small frags off the opposite side of the coral before it was all gone. The frags are growing nicely. That one took overnight to completely mush the coral. I know the water was not optimal in that tank (my nano). Other corals weren't doing really well; and when the cap died, it made the water a bit 'yucky' - and a couple of other corals shut down for a while. Several water changes later, the rest were fine.

 

STN I have a lot more experience with - but no more explanations. I can generally tell if a coral is STN'ing because from a point or points - the tissue on the corals just slowly disappears, and the bare coral skeleton turns green. Let me go get a picture...

 

This is my acropora Tenuis - which has been STN'ing for 6 months. The coral ALMOST grows fast enough to keep ahead of it. I call it VVSTN - very very slow tissue necrosis. Someone told me to check for Acro-eating flatworms, so I cut several branches and looked at them under the best magnification I could find (no scanning electron microscopes in my house). No sign of any kind of bugs or worms.

 

Quite often, STN will STOP after a few days or a week - taking just part of the coral. One millipora of mine started to STN; I cut off some large frags. It continued to STN, until there was a 1/2" square patch of live coral on one side of the base. Then it started to grow back - and is now covering about 2 square inches. The frags are fine - I've given a few of them away.

 

And there you have my experience; which is limited after only 1 year in the hobby. But still no real knowledge of what causes it, or what to do about it.

 

bob

[davelin315]

Rapid and Slow Tissue Necrosis. Necrosis is basically a condition where the tissue sloughs off the skeleton because it is dying. RTN occurs very quickly and you could lose a colony in less than an hour while STN occurs much slower and could take days or weeks to completely kill your coral. It's much different than bleaching where a coral expels its zooxanthellae and therefore loses its ability to manufacture food for itself through photosynthesis, this is where it is actually losing tissue itself and it basically peels away. There are a number of generally accepted theories as to why it takes place, ranging from stress to bacterial, protozoan, or parasitic infection, but there is often no explanation as to why it happens. It typically originates where there is an injury of some sort and then spreads to the rest of the coral. The typical action is to frag off whatever you can or frag off enough of the skeleton close to where the necrotic tissue is to attempt to save what remains, but more often than not when it is RTN it's too late already. STN is much slower but just as painful to watch as often it is also too late once it gets started. You do have a much better shot, though, of containing it if it's STN.

 

There are theories as to whether this spreads from one coral to the other, I have yet to see anyone prove that it does, though. More often than not, if two corals are RTNing at about the same time, it's because they have both been exposed to the same environmental conditions rather than them passing it from one to the other.

[txaggies07]

Thanks guys. Good info.