roe, milt, fish eggs
鮞 centers on fish reproductive material: roe, milt, or fish eggs. The meanings are tightly clustered around this specific biological concept.
鮞 combines 魚 (fish) with 而, which likely contributes the sound and may relate to softness or pliancy, fitting the texture of roe or milt. The exact historical development is uncertain.
The fish radical 魚 on the left and the soft-looking 而 on the right suggest the delicate, granular mass of fish eggs or milt inside a fish.
For ジ, imagine a fish releasing a stream of roe that spells out the letter 'G' in the water: G -> ジ, and the roe forms the shape.