a type of fish
鰄 refers to a specific type of fish. The meaning is narrow and concrete, without broader abstract extensions.
鰄 combines the fish radical 魚 with 威, which likely contributes the sound イ. The character was created to name a specific fish, but the exact historical development is uncertain.
The fish radical 魚 on the left tells you it's a fish. The right side 威 looks like a powerful, imposing shape, so imagine a fish with a commanding presence—鰄 is that type of fish.
For イ, picture an eagle (イーグル) swooping down to catch this fish: eagle -> イ, and the fish is the one being caught.