both danio's and tetra's are egg scatterers and plecs also lay eggs (no idea about sharks I'm afraid) so it could've been any of them to be honest.
Eggs are normally covered in a sticky residue when they are first laid (going by my cory eggs anyway) so it will be this residue that has been left behind on the glass.
It would possibly be better to ask one of the moderators to move this thread to the appropriate forum area where you will get better replies as this is the livebearers section and doesn't deal with egg layers
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thanks for the info,, will wait to see if they hatch and see what i get unless they get eaten