HRT TF
I'd imagine they'd be very tender right until they're done growing in. You'd have to take frequent baths to keep the muscles working, making sure you can breathe properly. Maybe keep wet towels wrapped around yourself, and making sure to swap them out when they dry out.
HRT TF
And when you're finished, and you can breathe underwater indefinitely~ imagine taking your first 24 hours underwater. And then imagine all the fun your partner is going to have kissing and brushing against those new gills of yours~