I have a Sen with a bent spine. He wobbles when he picks up speed, but otherwise seems happy. I'd stop with the freeze dried foods and switch to frozen. Much more nutritious.
He's doing much better! I put him in a quarantine for a week to make sure he was well fed and had perfect water and his swimming has improved greatly. He's improved so much that I've actually caught him bullying the other bichirs! Lol. He still can't swim quite as well as the others but he's no longer shaped like a banana like he was before.