DAY 3 UPDATE
Here is my late update on my rescue, today I did a 100% water change on his 2.5 gallon tank. He ate 3 separate tiny meals, and he seems to be alert. I check on him all day and when he is at the bottom I feel panicked that he mostly rests on his face :( I keep forgetting the lack of fins he has and gets pulled with the slightest current so I have to be very gentle with him.
I see clear fin regrowth on his caudal fin and that makes me happy, but I wish it could go faster for him, I hate to see his back so awkward.
Here are the latest pictures of him.