Parasitic copepod is my guess. My purple firefish had one and lived for years with it. I tried FW baths and extracting it with tweezers to no avail. Good luck.
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Lyretail anthais (F), purple queen anthias (M), desjardini tang, swalesi basslet, green mandarin, fridmani pseudochromis, rhomboid wrasse, lineatus wrasse, marble wrasse, Lubbock's wrasse
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