Paul Greenberg’s love of fish began at an early age and is deeply intertwined with a love of the outdoors; for him, an avid fisherman, fish are wild fish. Yet with fisheries worldwide collapsing from overharvesting, fish farming has emerged as a sustainable alternative. But is it? And are the Four Fish (Penguin, $16) that currently dominate the seafood market—salmon, sea bass, cod, and tuna—the best prospects for aquaculture?  Greenberg considers the overarching question of sustainability by examining each of these fish in turn; his enthusiastic and illuminating profiles include a survey of the role each species has played in human history, its own (often amazing) natural attributes, and its viability as a farmed species. Salmon, for instance, are capable of swimming prodigious distances. Is a wild salmon, with its fully developed muscles, really the same as a farmed salmon, bred in a cage with little room to move? Luckily, Greenberg knows there are more than just these four fish in the sea, and his introductions of previously overlook species such as barramundi, Vietnamese tra, African tilapia, and Hawaiian kahala are fascinating and offer real hope for the future.