Forty years ago, the Nile perch was introduced to Lake Victoria, the vast freshwater lake that unites the borders of Uganda, Kenya, and Tanzania. There, in a region some believe the birthplace of mankind, the implacable predator thrived like a cancer, gobbling up the native species. Biodiversity was gradually extinguished; oxygen levels plummeted; the lake’s ecosystem began to collapse. Lake Victoria is now in the death throes of an environmental endgame: With the food supply all but vanished, the perch has taken to feeding on its young.

But here’s the grim irony: The Nile perch has proved an economic boon to the region. Here’s another: While the Nile perch is being fished, filleted, and hauled off in huge cargo planes for the markets of the West, Tanzania is on the verge of famine.

In “Darwin’s Nightmare,” an intricate, chilling documentary now playing at the IFC Center, filmmaker Hubert Sauper shows us apocalypse now. We visit a maggot-infested garbage dump, where the rotting fish parts discarded by the factories are collected by local Tanzanians to be deep-fried for consumption. We watch as the orphans of fishermen killed by AIDS viciously fight over handfuls of rice and slump unconscious in alleyways after sniffing a homemade glue they’ve melted down from the plastic packaging used to export Nile perch.

We meet a man who makes $1 a night guarding a fishery with poison-tipped arrows. He hopes for the outbreak of war since the pay is better. We meet a Christian priest terribly resigned to the notion, writ large all around him, of survival of the fittest. His flock is ravaged by AIDS, but in deference to God’s will he refuses to educate them about condoms. We meet an optimistic prostitute who makes her living off visiting pilots. By the end of the film she will have been stabbed to death by a client.

Why expose yourself to this catalog of horrors? The social conscience would answer that we have an obligation to bear witness. The nightmare is ours: “Darwin’s Nightmare” is a ferocious expose of globalization’s sinister underbelly. While Mr. Sauper sometimes bites off more than he can chew, scoring easy points through didactic montage and not quite connecting all the dots, his image of total exploitation lands with the force of truth revealed rather than manufactured.

The more compelling, and troubling answer is that “Darwin’s Nightmare” is a stylistic tour de force. Like Werner Herzog and Chris Marker, Mr. Sauper is keen to harness the weird image, uncanny light source, or weird juxtaposition that will push the documentary form toward something hallucinatory, almost visionary. The result has been compared, not unreasonably, to science fiction or horror cinema, and one might also align it with the paintings of Max Ernst, “Los Olvidados,” and the infernal lyricism of William S. Burroughs.

Such aestheticism releases a horde of ethical and moral hobgoblins. We can argue over the ethics of representation till we’re blue in the face. In the meantime, Tanzania is choking to death. The unrelenting visual grip of “Darwin’s Nightmare” is justified in this: It grabs hold of that prefer to stay averted.