Thanks so much guys! Yes, the split where sushi indicated is what i was concerned about. The ruffliness has been there since i got him, the pet store said it was normal for bettas, so i wasn't worried. Here's a better pic, of that area for your expert opinion:
Dorsal fin:

Tailfin

I think he looks ok - nothing like the pic that Mr B helpfully suppllied

- but i'm hoping you'll agree with me. I want to have salt in with him on a regular basis (2 teaspoons for the 5 gallon tank?) as recommended on a betta site that i really like. Maybe this will be enough to keep him safe.
Thanks again for all your help!
Dana.