There aren't many good fish cookbooks. Trust me. This one is priceless.
Buy & read this book. It's that easy. This is probably the best fish cookbook to have at your disposal. I can count on one hand the number of seafood books that actually tackle the issues that matter to the professional chef. Peterson is not afraid to address those issues and it shows in Fish & Shellfish. Fish names alone can kill the normal text that tries to teach fish cookery. Did you know the Chilean sea bass isn't even a bass? It's real name is the Patagonian Toothfish. Muliply that instance a hundredfold and you'll begin to see my point.
He takes a similar descriptive stance as he did in Sauces, with ethnic recipe breakdowns, generally starting with French or American, and then giving Italian, Asian, and others a healthy respect. Coupled with his other books, it's very easy to improvise a meal with what you have on hand. I'd dare someone to say something negative about this book, it's purely educational.