shark family, including some rays and skates
魦 centers on the shark family of fish, including some rays and skates. It is a specific zoological term rather than a general fish character.
魦 combines 魚 (fish) with 少, which likely contributes the sound. The exact historical development is uncertain, but the structure suggests a phono-semantic compound for a type of fish.
The left side is a fish 魚, and the right side 少 looks like a small, sleek shape. Picture a small but fierce fish gliding through the water: a shark.
For サ, imagine a shark swimming in the Sahara of the ocean: Sahara -> サ, and the shark is the king of this sandy underwater desert.