Is this a oxymoron?

"While his gills were breathing in the terrible oxygen"

is this a personification?

"He didn't fight, he hadn't fought at all" (talking about a fish)

An oxymoron is a combination of words that contradict eachother (ex: jumbo shrimp), so no, I don't think the first sentence is an oxymoron.

The second sentence isn't really personfication, because personfication is giving inanimate objects or animals human traits, like saying the wind whistled. Fighting isn't necessarily a human trait, animals fight and hesitate to fight often.