fish bones, honest, upright
鯁 centers on the idea of something rigid and obstructive, like a fish bone stuck in the throat. The meanings 'honest' and 'upright' extend this as a metaphor for a person who is stiffly principled and unyielding.
鯁 combines 魚 (fish) with 更, which likely contributes the sound and the idea of something hard or obstructive. The character originally referred to fish bones, with the abstract meanings developing later.
A fish (魚) with a hard, obstructive bone (更 suggests hardness) stuck inside: that's 鯁, a fish bone. An honest, upright person is like that bone—stiff and unyielding.
For コウ, imagine a fish bone so hard it makes a 'koh' sound when you tap it: koh -> コウ. The bone is as rigid as an honest person's principles.