It is commonly called pitting, and while some infections can cause it it also has to do with the oscar's food. Make sure he is on high quality food and don't spoil him with feeder fish as these are a main cause of it.
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55gal,260 watt PC(2x65 actinic,2x65 10k daylight,8 lunar LED) 45#LR, 45#LS, 3 maxi-jet 900's on a natural wavemaker timer,phosban reactor, 5 gal fuge (built out of standard 10 gallon tank) with chaeto, grape, and feather caulerpa, sealife systems protein skimmer, wet/dry, 4 blue/green chromi, 1 skunk cleaner shrimp, 2 lyretail anthias, 1 royal gramma,1 true perc 5 mexican turbo snails, assorted dwarf blue leg hermits, astrea snails, and nerite snails |