Devonian period is also known as: 

The correct answer is Golden age of Fishes.

Important Points

• The Devonian is a period of the Paleozoic Period.
• Fish reached substantial diversity during this time, leading the Devonian and thus called as "Age of Fish".
• The first ray-finned and lobe-finned bony fish appeared and placoderms began dominating almost every known aquatic environment in this period and thus called as the golden age of fishes. 

So, the Devonian period is also known as the Golden age of Fishes.