flatfish, turbot, cod
鰔 centers on specific types of fish: flatfish, turbot, and cod. These are distinct fish species, so the core idea is simply a fish name rather than a single conceptual thread.
鰔 combines 魚 (fish) with 咸, which likely contributes the sound. The exact historical development is uncertain, but it is a typical phono-semantic compound for a fish name.
The left side 魚 means fish, and the right side 咸 looks like a container with a spear. Imagine a flatfish, turbot, or cod being caught and stored in a container: 鰔 is a fish.
For カン, picture a can of cod: can -> カン, and the fish 鰔 is inside the can.