salamander, female whale, small fish, old person's teeth
鯢 centers on a salamander-like aquatic creature, with extended meanings that are rare or archaic: a female whale, a small fish, or an old person's teeth. These senses do not share one clear conceptual center; the salamander meaning is the primary modern usage.
鯢 combines 魚 (fish) with 兒, which likely contributes the sound. The character originally referred to a salamander or a type of aquatic creature. The extended meanings are rare and their historical development is uncertain.
The left side 魚 means fish, and the right side 兒 looks like a child. Imagine a fish-like creature that looks like a child's drawing: a salamander with a big head and wavy tail.
For ゲイ, picture a salamander dressed as a geisha (ゲイシャ) performing a dance: gei -> ゲイ, and the salamander's movements are graceful.