What period of the paleozoic era is known as the "age of fishes"?

The Devonian Period.

This period is named after Devon, England because this is where the old red sandstone of the Devonian was first analyzed and studied. This period was known as the age of fishes because it spawned a large variety of fish. For instance, most of them were armored placoderms that had powerful jaws as well as blade like plates that acted as teeth.

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a is the answer i believe.