Its poop that didnt get fully digested before it got pooped out. Probably because who ever you had feeding them feed way to much, so it just got shoved out. My cousin has two oscars and he over feeds them i see similar looking stuff in his tank all the time
I was feeding the ray again this morning and gave it an entire shrimp in small pieces and surely enough similar stuff was pooped out shortly after. Seems to be the explanation. Good news is its nothing to worrry about bad news is I should feed it less
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