No fish is so intelligent as the simplest bird.

I would not bet my money on it. In some areas fishes can score higher than many other vertebrates for sure, including big apes

Anybody keeping an aquarium knows that many fishes are surprisingly smart. Specially predatory fishes. They have a good long term memory and can recognize individual caretaker humans.

The brain/bodyweight ratio of some species is bigger than humans. This mean that they have a bigger brain that most birds, lizards and rodents of the same size. Sharks are pretty clever for example.

A very good question - I do feel differently about fish, and I think it's the relative level of intelligence.

As you suggest, it's clearly not just because birds have an ability to explore an environment natively that humans don't.

I'm sure that's a bias towards similarities with human intelligence - to communicate, solve puzzles, and use tools (e.g. crows and parrots) because it would be very sad if people were regularly keeping octopuses in home fish tanks.