fish name
魲 is a rare kanji used as a name for a specific fish. Its standalone meaning is limited to this fish name, with no broader conceptual center.
魲 combines the fish radical 魚 with 户, likely as a phono-semantic compound where 户 hints at the sound and 魚 indicates a fish. The exact historical development is uncertain.
The left side 魚 means fish, and the right side 户 looks like a door. Imagine a fish named after a door, perhaps a flat fish that resembles a sliding door.
For ロ, picture a fish swimming in a low, narrow stream: low -> ロ, and the fish is the 魲.