This is my new boy, Crusoe. He is active and healthy but has that strange thing on his tail. Although it looks like a hole, his tail is part cellophane and I've checked and am 100% certain that there IS fin in that area, no hole whatsoever.
He has had this mysterious thing since I found him in the pet store three days ago. It curls to one side and does not flow like the rest of his fins do when moving. As you can see, it looks brownish and stiff. This is the only spot he has it and I was wondering what it is. When I first saw it I thought Fin Rot. However, it is not melted looking and NO part of him anywhere is looking frayed, shredded, melted, or is missing for that matter.
Could it perhaps be a problem or is it a strange thing that he was born with?
Since I've had him, he's been in water at a steady 78 degrees with some aquarium salt added to help relieve stress and perhaps even help that tail ailment. He has already made a bubble nest and does not show any signs of sickness. He wasn't even nervous or lethargic when I first put him in his tank, just active and explorative. I never saw a fish transition so perfectly, which is why I wonder if it is a problem at all.
It's quite common when fish have gotten a damaged fin, or have been in ammonia sludge. My ol' boy Georgie, his fins looked like crinkled tissue paper - and they somewhat still do. It's from ammonia as he lived with goldies all his life!
Then my cellophone Voldemort, he got it from when he chewed his fins. So did El Dorado, and even Spartan near the end of his life because his tail was munched on.
I would stop the salt treatment, mainly because a damaged fin is usually nothing to run out and medicate - it usually clears up with warm and clean water (like Georgie's fins which have gotten 50% better) or if it doesn't, it's just a peculiar mark that'll be there for his life.
It doesn't look like a problem~ Portal Prime had something like that on his bottom fin as well but it had curled up from being in his cup for a long time. But on yours it looks like it kind of grew that way o.o
As long as it isn't life threatening or health threatening, I don't mind. I like his curly tail, its cute. I had a feeling the ammonia must have been high because he was swimming in poop when I got him, though it wasn't too bad, and PetSmart was hesitant to let me test his water. If I wasn't short on time and they would have done so quickly, I would have.
Thanks Zack! He was an amazing PetSmart find. I had sworn that I was going to find either an orange or a yellow as my next betta...so of course they had both and I had to choose. He's got so much personality, though, I had to go with him. I'm glad it isn't anything serious. I just like to double check.
Thanks Sena! Its always better to be safe than sorry and I always value as many opinions as possible. I never saw this before and although I thought it was cute, I didn't want to ignored it just incase it wasn't so cute after all.
I know what you mean! Part of Georgie's dorsal is still crinkly, but it'll be permanent I've attached a picture so you can see what I mean about his fins... I've seen it sadly, so many times! but it's what I do :p The dorsal is what is seen in this one, and where it "folds over" it's really ust crinkled. He's begun biting his caudal, but I expected that when it would thicken again.
My boy Champagne has the same thing, in his anal, dorsal and ventral fins. Aside from occassional fin splitting, he doesn't have any trouble. It's mostly a cosmetic issue. Just keep his water clean, clean, clean.
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I've attached a picture so you can see what I mean about his fins... I've seen it sadly, so many times! 
