I ate fish almost everyday (except had to choose chateau Briand for one dinner) on the RCCL cruise last week, on Oasis of the Seas ship, and had zero problems with anything, including food.
I take RCCL cruises often. Almost always have a good experience. There was one time in 1987 (my honeymoon) where my bride and I got violently sick for a 2-3 day period. I'm pretty sure it was the raw fish we had during a midnight buffet. But we'll never know for sure. And we had no idea if others got sick too. But the crew of the ship were phenomenal during that time. They felt bad we got ill and were always checking on us and bringing us food to our cabin. When we felt better, they slipped us an envelope of gift certificates to use at the next port of call.
We never complained and ended up becoming loyal customers of the line as a result of how great they handled the situation.