This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
鮲 combines 魚 (fish) with 伏, but the exact historical development and original meaning are uncertain. It may be a phono-semantic compound, but no clear evidence is available.
Since the meaning is unclear, focus on the shape: a fish 魚 beside a person 亻 and dog 犬 (伏). Picture a person hiding a fish from a dog.
For モテ, imagine a fish that is so popular it's always being chased: モテ (mote) as in モテる (to be popular). The fish is popular with both people and dogs.