Japanese dace
鯎 refers specifically to the Japanese dace, a type of freshwater fish. Its meaning is a single concrete species name rather than a broad conceptual idea.
鯎 is a Japanese kokuji (国字) created by combining the fish radical 魚 with the phonetic component 成, likely chosen for its sound to represent the native word うぐい.
The left side 魚 means fish, and the right side 成 can suggest 'becoming' or 'achieving'. Imagine a fish that becomes a dace when it grows up: 鯎 is the Japanese dace.
For うぐい, picture a dace swimming in a clear stream, and a child pointing and saying 'Ooh, gooey!' (うぐい) because the fish looks slippery. The 'ooh-gooey' sound hooks the reading うぐい.