In the mid-1960s, a new species of fish, the Nile perch, was introduced in Lake Victoria, Africa’s largest. In the mid-1990s, Austrian filmmaker Hubert Sauper went to the shores of the lake, in Tanzania, to film how the species, now one of the country’s main exports, had obliterated all others in the lake and even became cannibalistic. In the mid-2000s, the film “Darwin’s Nightmare” (204, 107 min) opened at the Venice Film Festival, shocked audiences worldwide, and has since been nominated as Best Documentary at the Academy Awards.