Can you help me identify this teen / YA book? Pass an exam or turn into a fish

[deplorabelle]

Hi all

My DS has been told by his school librarian about a book he's interested in but has forgotten all the details of it.

Apparently the premise of the book is that at the age of 15, everyone must pass an exam to remain human. Fail, and you are turned into a fish.

Does this ring any bells with anyone? Some googling hasn't turned anything up; partly because I don't really know what I'm looking for

Anyone?

I think it’s probably ‘The Territory’ by Sarah Govett.

Only thing is, the teenagers don’t actually turn into fish - it’s just slang for being exiled into a super-malaria ridden swamp.

Ooo thank you that's the one!!