When compared with the personalities of other animals. . . a fish, even the salmon, hardly registers""--and yet Caras, who has so gracefully recorded the life histories and survival strategies of the Kodiak bear, the wolf and the California condor, seems almost mesmerized with the silvery perfection and the ""chemical memory"" of Oncorhynchus nerka, the Pacific salmon which begins as an alevin in the gravel bed of a small stream and grows to become a fry, parr, fingerling and smolt before it receives the biological signal to migrate away from the lake to the ocean. It will spend most of its life--anywhere from two to seven years--in the ocean before returning to the river bed of its birth to spawn and die. Of the 3600 eggs hatched by a female sockeye only two will live to complete the cycle. To make the transition from fresh to salt water, Nerka will repace all his bodily processes; on his return voyage he will change from silvery slate to bright red. How does he navigate? Do his watery cues come from magnetism, gravity, electrical fields? From the salinity of the water, the sun or the moon? Caras tends to wax eloquent when talking of ""cosmic clocks"" and ""grand designs"" and the ""immortality"" and ""perfection"" of the sockeye--but the mystery of his life and death is real enough and who can deny that Nerka's fate, from hatching to final frenzied spawning run, is as improbable as anything in nature's constellation.