Sadly if the fish is not eating it will end up dying. The trick of the game is to get it to eat. Irrelevant of what the internal issues are. What I have seen over the past two years, are clowns that don’t eat because of parasites, stress, or internal organ damage. Without a good microscope and knowledge what to look for (not saying you’re not a smart person, but having an idea what to look for and at what zoom is a factor in translating the data you’re looking at) you will miss what the issue can possibly be.
What I’m getting at with the trick being to get the fish to eat, it’s how it will continue to live, yes I know I’m pointing out the obvious haha (call me captain obvious! Haha!) , but hang in there with me. So if the fish starts eating it will have strength keep fighting. Also the immunity might build back up to fight off the internal issues. Then transition to feeding some meds by 1% of body weight if you can make this happen. Last resort that I have done is force feed with real tiny feeder tubes. Some fish are too small for these to. This is real tricky though being you have to make the judgment call on if the fish is large enough. There are small needle silicone (I think) based tubes. Then amount of food and meds to put in the fish is another trick.
Internal organ damage can happen from many things, one is hitting objects in the tank or glass from being started. Aggression fights, had a black ocelaris that didn’t even show signs of any external damage until I looked at her face closely and saw the hit to her nose. She was being chased and hit the glass I would presume. Ended up just like your fish unfortunately, and I hand to put her down. She ended up pooping the same and exterior showed nothing else to be an issue. I do have a microscope and have the knowledge what to look for in regard to internal issues. The feces was cleared of anything.
Aggression stress, I have seen this sometimes without much external damage, but the presence of another fish, maybe bigger, set off a major stress factor for a smaller fish, and slowly the smaller withered away into hiding and not eating. This was a black cap basslet. I had to remove the fish, and live it some times to gain courage I would say. It’s already a shy fish that you have to keep a close eye on, and what tank mates you put in, if hiding spots are not abundant. About a week ago the black cap started eating again and doing well. This started with it when I introduced a 4” powder blue hybrid. The tangs energy was too much for him and he basically shut down. It was crazy to see! And mind you the tank is a 150. But during feeding time tangs can go nuts after food. Then there is the physical attacks on fish that can take place and one fish will damage the other internal even from head bunting it, and other things of this nature. This can also cause internal organ damage similar to just hitting objects in a tank. But this one’s visible. And can be caught early on most of the time before aggression really does damage. The signs of bit marks, fins nipped and so on.
Sorry for the long write up, but having dealt with a few non eating clowns, some made it some didn’t. My last success story is a maroon that did this, life brine shrimp got her going after food, then black worms got her in pace to eat normally after about 2 months of back and forth.
