huge sea turtle
鰲 centers on a huge sea turtle, a mythical or giant marine creature.
鰲 combines 敖 (phonetic and possibly suggesting large or proud) with 魚 (fish), indicating a large sea creature. The exact historical development is uncertain, but it likely originated as a character for a mythical giant turtle.
The top part 敖 looks like a proud, towering figure, and the bottom 魚 is a fish. Together they form a giant sea turtle rising from the ocean like a proud fish-king.
For ゴウ, imagine a huge sea turtle going 'GOU!' as it surfaces with a mighty roar: GOU -> ゴウ.