@vetteguy53081@Jay Hemdal may be able to help. Can you give us more on what you think the issue is as well as tank age, parameters, fish age, and QT status.
Bacterial infection. Unfortunately, these are not very forgiving fish and any treatment may or may not work at this stage. Diagnosing bacterial diseases and why they occur is not always a simple, straight forward task. Bacterial infections can stem from many causes, even combinations of contributing causes, and can be topical . . . internal, external or both. Healthy fish have a strong, natural resistance to bacteria and can usually fight it off on their own, but weak, sick and/or stressed fish can be very susceptible to this illness. The tiny open pores of the lateral line or open wounds are most often the point of entry for the onset of internal infections, but the soft tissues of the gills are also a prime entry point.
You may then ask as in case with your fish, what caused it. Some causes are :
Poor environmental conditions. If conditions are poor enough, the bacteria can bloom and overrun even the healthiest of fish. White cloudy water with the presence of sores on the fish can be signs of this problem.
A secondary infection resulting from having another disease. An excellent example of this is the open sore left by a parasite infection, such as cryptocaryn. In many cases, the fish has been cured of the parasite, but the resultant infection from bacteria entering the fish's body via the break in the skin will cause death
Poor nutrition
Injury, such as open wounds, cuts or scrapes
Harassment from other tankmates
Stress
Weakness
Common symptoms are :
Reddened and frayed fins, or red streaks through the fins. Red fins are often a sign of ammonia burn, which can be caused by poor packing procedures during shipping or again- water quality.
The disintegration of the fins, fin and tail rot.
Redness around the area of the lateral line, often seen as streaks or blotches
Open sores on the sides of the body and near the fins
Bloody scales at the base of the fins
Rapid breathing
A gray film over bulging eyes
Listlessness or lethargy
Loss of appetite
Abdominal swelling or bloating
For treatment, Maracyn 2 is mincycline hydrochlor based and is a gram-negative bacteria treatment, as well as sufficiently absorbed through the skin to treat internal infections. Since most bacteria that cause disease in marine fish are gram-negative and can quickly become systemic, Maracyn 2 would be the most effective choice. This should be done in quarantine. Increase oxygen during treatment , even with an airstone.
Looks like it is pretty thin and is resting on the bottom? If so, there probably isn't much to be done for it. It could be a bacterial infection, but if it is newly imported, it could also have a protozoan called Uronema.
At this point, you want to be in damage control - are their other fish in with it? You'll want to ensure they aren't going to go down the same road.
It would help to have some background info on the tank and the fish:
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