Sous Vide White fish 30mins @ 60c

I've used those "frozen fish in a pouch" products, that you shove in the oven. I quite like them, but they have too much butter, or what I think is butter, in them. When I thought of doing sous vide fish it was along similar lines. The reality, as I'm discovering more the more I use it, is different using the water bath.
I took some frozen white fish portions and bagged them with some butter. I allowed them to defrost in the fridge for 24hrs.
I looked up a temperature that others had used and decided that around 56°c was good, for around 30mins. When I took them out of the bag it was possible to pick them up with my fingers, they seemed quite cool. There was a lot of liquid in the bag, which I suppose was ice, together with the butter.
The fish seemed quite raw as some parts of it were still quite transparent. This would be ok if the fish was fresh, but I was a bit dubious of the frozen stuff. It tasted fine though.
I did another batch a few days later, this time I did them without butter, at 60°c for around 30mins.
These were whiter, the proteins had firmed, and the flesh was flakeyer. I preferred this texture for this fish, but I'd probably do fresh fish lower and then maybe finish in butter in a pan.