How we identifying phatogen just by microscope

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Hello, i am a new member here. today i just found my emperor anglefish was blind in its eyes. it so blind awful, but the fish still breathing and swimming normally and there's no frayed or haemorrhage on fins. then i tried to look those slime under 4x magnification. here, i attaching picture of phatogen i have found. may y'll could helping me. thanks in advance