Question

How does a lair apply to a school of fish??

Answer 1

 I've never heard the word "lair" applied to fish. Usually "lair" means the place (like a den or burrow) where a mammal such as a wolf or bear hangs out. 

Some fish like to hole up in caves, but in general those are not schooling fish, so you would not find a school of fish in a lair, for the most part.