The much maligned brook trout gets star billing in this encyclopedic, readable study of Salvelinus fontinalis from Newsday outdoor columnist Karas. Many anglers give the brook trout a bum rap, considering it an inferior quarry to the wily, fighting browns and rainbows. But there is also a dedicated band of brook trout fanciers, who find in this exquisite fish--decked out in black and olive, rose and pearl, accessorized with light green shading to yellow squiggles and vermilion dots haloed in powder blue--the very stuff of our continent's angling past, a synecdoche testifying to clear, cold, pure waters, to a life pristine and unpretentious. Karas is decidedly in the latter group, his book a labor of love: ""Our relationship with this unique fish has never been fully documented or evaluated,"" he writes. It has been now. Karas goes back into the mists of paleoichthyology to get a handle on beginnings; charts distribution in post-glacial times; scrutinizes species, subspecies, strains (the brook isn't a trout but a char); offloads a bargeful of fish stories. The author devotes the majority of the book to the history of brook trout fishing in New York and Canada, from remote headwaters to rivers the mention of which--Nipigon and Minipi and Ashuanipi--get brook-trouters in a lather; and closes with the rude effects of acid rain on wild trout waters, this after logging and mining had already trashed the habitat. This is the kind of book anglers long for: smartly written, free of hyperbole, full of obscure historical tidbits, laced with snatches from old diaries and letters, and enticingly informative (from mere clues to gifthorse treats) on how and where to fish for wild brook trout today. Angling literature, burdened as it is by overproduction, has every reason to celebrate Karas's brook trout encomium.