The only fishing novel I can think of is A River Runs Through It by ??. I've never read it myself, but remember watching the movie. Not sure if it's something a 13 year old boy would be interested in, or not.

Maureen, you don't say if your son is into sea/coarse/fly fishing. My DD, who has recently taken up trout fishing read and enjoyed Salmon Fishing in the Yemen by Paul Torday and A River Runs Through It by Norman Maclean (a film was made of it). These might not be totally suitable for a 13 year old.
Many UK book sites highly recommend Mr Crabtree Goes Fishing by Bernard Venables. Quite an old publication and produced in 'cartoon' form (it originally appeared as a newspaper series). Something a youngster can pick up and enjoy and keep returning to; with excellent illustrations.

Here is a link that might be useful: A Favourite Fishing Book

Not exactly fishing stories, but there are three which spring to mind.

The first is Coming Up for Air by George Orwell - the "hero" describes very well a youthful passion for fishing. It's also a brilliant book, and perfectly accessible for a bright lad. If he can read TOMATS, he can read Coming Up for Air.

The second is Three Men in a Boat by Jerome K Jerome, which has a very funny chapter about fishing - or at least about a particular fish.

And the final one, of course, is Izaac Walton's Compleat Angler, which is self-explanatory.

?

Three mysteries that revolve around fishing
: Ngaio Marsh Scales of Justice (a reference to adultery, but it was originally written in 1955, so pretty tame.)
Cyril Hare Death is No Sportsman Also some adultery involved in the murder-but originally written in 1938, so even tamer.
M.C. Beaton:Death of a Gossip noted gossip columnist murdered while learning to salmon fish as a Scottish fishing school.

I read all three a while ago, but as I remember them, fishing is a main part of the story, with technical details involved in solving the crime.

don't know why the question mark is floating in my post above-I didn't put it there.

I seem to remember that in Nick Adams Stories by Ernest Hemingway there are a few short stories about fishing and hunting

Here is a link that might be useful: Nick Adam Stories

Thank you for all the suggestions. I have also found out that Zane Grey wrote some well-regarded true tales about fishing. My brother loved his westerns when he was young.