It is definitely circa 1950s Murano glass. It is most probably by Alfredo Barbini, either for his own company, Cenedese or even his earlier incarnation at VAMSA (although I'd vote Barbini for Cendese).
I don't see anything at all out of the ordinary in the fish as far as their being from Murano. I have seen dozens of variations on this centerpiece, and there are photos of these types of bowls and centerpieces in the literature.
Laura