sole, flatfish, flounder
鰈 centers on a type of flatfish: sole, flounder, or similar bottom-dwelling fish with both eyes on one side.
鰈 combines 魚 (fish) with 枼, which likely contributes the sound and may relate to thin, flat objects, fitting the flatfish meaning.
The left side is a fish 魚, and the right side 枼 looks like a flat, layered object. Imagine a flatfish lying on the ocean floor, its body as thin as a leaf.
For チョウ, picture a flatfish named Chou, who is the flattest fish in the sea: Chou -> チョウ, and its flat body matches the kanji's meaning.
righteye flounder (any fish of family Pleuronectidae)
slime flounder (Microstomus achne)
dab; small plaice
Kamchatka flounder (Atheresthes evermanni)
starry flounder (Platichthys stellatus)
slime flounder (Microstomus achne)
marbled sole (Pleuronectes yokohamae)
brown sole (Pleuronectes herzensteini)
stone flounder (Kareius bicoloratus)
roundnose flounder (Eopsetta grigorjewi)
Alaska plaice (Pleuronectes quadrituberculatus)
flathead flounder (Hippoglossoides dubius)