Anyone know what this is?

[pacificdiver]

I have a yellow tang that experienced a rapid decline in the DT, presumably because I was running carbon more than it could tolerate, though I thought it would be well below what would cause problems (3 days per month).

I removed him to QT and he's improved dramatically in the space of about 10 days, but can anyone identify the discolored spot at the rear base of the dorsal fin? Most of the affected dorsal and ventral fins have grown back, but regrowth appears to be "stuck" at the rear base of the dorsal fin, near the discolored area. It looks like there's more of the same discoloration near the top of the dorsal spines as well. This discoloration was not present when the fish was introduced into QT.

He's been in a 20G QT with only mechanical/biological filtration. I added Maracyn2 according to the package instructions, and have been doing daily water changes of about 4 gallons, replacing the Marcyn2 with each w/c.

**Please note that the photo was taken about 3 hours after lights off, so the discoloration of the main body is normal and not part of my question.

Thanks in advance.

[HumbleFish]

He looks to have some HLLE around the eye. The dark spot could be a bacterial infection. Is it getting any better by dosing Maracyn 2?

[pacificdiver]

Originally Posted by HumbleFish

He looks to have some HLLE around the eye. The dark spot could be a bacterial infection. Is it getting any better by dosing Maracyn 2?

The fins affected by the HLLE seemed to improve rapidly, but the discoloration on the fins showed up after being introduced into QT with Maracyn2 and small feedings 2/day with Selcon soaked nori and pellets. I've attached photos from day 1 (left) and day 10 (today). I have Furan2 as well. Would adding Furan2 be a logical step? I was suspecting necrotic fin tissue, but I've never seen it before, so I don't know what it would look like.

The fish is a bit nervous in QT, but he's feeding strongly and shows a dominant fin stance, so I'm reluctant to do anything too drastic here. At the same time, I don't want to let it get any worse. I have malachite green and Paraguard on hand. Wondering if either of those might be beneficial for a dip, or if it would be better to just watch it.

I've heard of situations in which necrotic tissue needed to be cut or scraped away. For obvious reasons, I'm reluctant to do anything of the sort, but if it's what needs to be done, I would be open to it.

Any advice would be greatly appreciated. Thanks in advance.

[HumbleFish]

Minocycline (Maracyn 2) isn't the best antibiotic to use in SW. I think you'd see better results from using Furan-2. You can also add Kanaplex + Metroplex to Furan-2 to widen the spectrum of treatment.

[pacificdiver]

Originally Posted by HumbleFish

Minocycline (Maracyn 2) isn't the best antibiotic to use in SW. I think you'd see better results from using Furan-2. You can also add Kanaplex + Metroplex to Furan-2 to widen the spectrum of treatment.

Great, thanks for the tip. I'm going to switch to Furan2 and get Kanalex and Metroplex on order. Thanks again.

In your opinion, am I likely correct in assuming this is some sort of necrosis?

[HumbleFish]

Originally Posted by pacificdiver

In your opinion, am I likely correct in assuming this is some sort of necrosis?

Most likely, but I think HLLE is the root cause.

Before you put him back in your DT, I would eliminate any possible causes: https://humble.fish/hlle/

[pacificdiver]

Originally Posted by HumbleFish

Most likely, but I think HLLE is the root cause.

Before you put him back in your DT, I would eliminate any possible causes: https://humble.fish/hlle/

Thanks, the rapid turnaround after being taken out of the display and the lack of improvement with water changes seems to definitely point toward HLLE as the underlying problem. I've removed all carbon from the DT, and will be using chaeto to bind up nutrients going forward instead of pulse-use carbon. I'm also going to do Selcon permanently - I had stopped for about 6 months, and I really shouldn't have.

I think I'm going to keep in QT for a couple of more weeks, at least until the darkened tips on the fins disappear. I wish I had taken him out sooner, but I was chasing the wrong problem, thinking it was water quality. I've only seen textbook obvious cases of HLLE, never one that affected the fins so much.

Thanks again for the input. I'll post an update in a week or so.

[HumbleFish]

Also feed lots of nori. That will help if the HLLE is due to a nutritional deficiency.

[jmicky41]

Yellow tangs don't seem to get the textbook looking HLLE (like you would see on a sailfin or purple tang) - usually it will look like what your yellow has.

[pacificdiver]

Originally Posted by jmicky41

Yellow tangs don't seem to get the textbook looking HLLE (like you would see on a sailfin or purple tang) - usually it will look like what your yellow has.

Thanks, I unfortunately had no idea it could look like this. I had no idea it could affect primary the fins, or I would have caught it sooner. It's a shame it got out of control while I was chasing the wrong issue. He seems to be getting better, but I want to get this brown spot resolved, since it seems to be holding still, or possibly worsening, while the rest of him improves.

[jmicky41]

Actually, I'm encouraged by the considerable regrowth of your tang's fins. Oftentimes, when the fins are that eroded they won't improve that much.

[pacificdiver]

Originally Posted by jmicky41

Actually, I'm encouraged by the considerable regrowth of your tang's fins. Oftentimes, when the fins are that eroded they won't improve that much.

Thanks, I was shocked at how quickly everything grew back. I was expecting several weeks, but it was actually days. It looks to me like the spot at the base of the dorsal fin may be scar tissue forming? Judging by the abrupt stoppage of regrowth at that spot, I'm thinking he'll be permanently bare from the spot backward. Time will tell, I suppose. Just thankful things have turned around for him.

[pacificdiver]

Originally Posted by jmicky41

Actually, I'm encouraged by the considerable regrowth of your tang's fins. Oftentimes, when the fins are that eroded they won't improve that much.

Looks like he's making quite a comeback. Still has some improving to do, but the dorsal and ventral fins are almost back to normal. I suspect the head scars will probably be a permanent reminder. The brown stained area at the base of the dorsal fin that I mentioned in the opening post appears to have been an area of rapid cell division, as it has followed the leading edge of the fin regrowth and subsided as the dorsal fin regrowth slowed down.

Thanks again to all who offered advice.