THEIR NATIVE WATERS span the Pacific Rim, from Kamchatka to Mexico, yet after years of artificial propagation and mass transport, rainbow trout now swim on every continent save Antarctica. They are among the hundred most invasive species in the world. In An Entirely Synthetic Fish, Anders Halverson traces the history, cultivation, and dissemination of rainbow trout, the politics of sport fishing, and various other well-intended programs with unintended consequences.

The global spread of the rainbow began in the 1870s when the newly formed United States Fish Commission hit California with the aim of propagating fish to replenish American waters, which had rapidly become devoid of fish due to the construction of dams, deforestation, pollution from sewage and mills, and overfishing. While Americans fished for food as much as for sport, it was the politics of sport not sustenance that fueled the rapid spread of trout around the world.

After the Civil War, sporting clubs touted outdoor recreation on fish-filled waters as essential for national healing. Nineteenth-century leaders in conservation, such as George Perkins Marsh, argued that outdoor recreation was integral to the American democratic spirit. In contrast to Europe, where rivers were often privatized for the elite classes, Marsh believed it was necessary to maintain public access to American waters so that anyone might enjoy nature. Based on an unwavering faith in public access and an aversion to potential environmental regulation, Marsh and the leaders of the United States Fish Commission believed simply putting more trout into American waters provided a viable means to simultaneously boosting fish populations and national spirit, and rainbows were their currency.

Halverson argues that the rainbow trout was an unassuming victor, its eventual domination fueled by ease of propagation and politics as much as advancements in long-distance travel. Thanks to refrigeration, trout ova were sailed to far-off waters of New Zealand, Patagonia, and Japan. Rainbows rode the rails, dropped from planes, and filled fishless waters around America. Even John Muir argued for spreading this fish around the West. He believed that more opportunities to fish for trout would create more constituents for wilderness.

But spreading the rainbow around America not only meant removing potential native competitors such as the Colorado pikeminnow, it meant tinkering with biology, creating a tough and tolerant species that was able to outcompete native fishes. Through repeated propagation and genetic mixing, rainbow trout have now become comparable to a genetically modified food crop. Naturally this has led to a host of problems. For example, whirling disease (a parasitic worm that inhibits fish mobility and growth, causing early death) now threatens entire populations, while crossbreeding with native cutthroat has made restoring and preserving native fishes difficult.

Despite this, state and federal agencies continue to propagate and stock more than 2 billion fish (40 million pounds) annually. It’s a familiar Catch-22—the revenue from license sales and equipment taxes from anglers is integral to the funding of programs aimed at restoring and protecting native species. While their role remains controversial, anglers are increasingly at the center of native fish and ecosystem restoration. And in the end, Halverson does not denigrate the fish nor the actions that have led to its global domination. Instead, he highlights lessons learned and acknowledges what Muir hoped for: anglers who fish for rainbows might in the end become advocates for native fish and their ecosystems.