Hello all, I’m new here, a sad first post. Many moons ago I kept a few aquariums wile in college, but haven’t for a while now. My son just set up a small aquarium with two guppies in June. I noticed today one is missing it’s dorsal fin. It looks either chewed off or eroded away. Its tail fin is a bit ragged but not stringy like what I’ve seen in fin rot photos. Is that what this is? I’m thinking it’s relatively recent as I haven’t noticed it before. It appears lively enough, doesn’t seem sluggish or anything, and eats ok when fed.