This was largely an experiment to see if i can get better texture from cooking frozen Grouper Sous Vide instead of traditional steaming. I will jump straight to the conclusion: the improvement was very good but still inadequate in comparison to steamed fresh fish. Also, it introduced another problem – the fish skin ended up undercooked. I guess the underlying problem remains the same, which is, frozen fishes are too dry to be suitable for doing Chinese traditional steamed fish. You should only do deep or pan frying with them.
Just for your information, i roughly based the cooking temperature and timing on a recipe meant for Cod fillets, cooking at 55°C for 30 minutes for a 600-700g whole Grouper.