Billy feels responsible for causing the apocalypse, and the two live in a dome built by Ray that protects them from the outside environment.

Ray stays up late one night, and discovers the possibility that the fish are undergoing sequential hermaphroditism to continue breeding, and notices a bright green light outside the dome.

Biosphere was written by Mel Eslyn and Mark Duplass, who got the outline for the plot when they attended a writers' retreat in 2018.

The website's consensus reads: "Biosphere's rambling, unfinished feel doesn't always serve its thoughtful themes, but it's often offset by the engaging interplay between the movie's well-matched leads.

[9] John DeFore of The Hollywood Reporter described it as "post-apocalyptic survival meets … anxious buddy humour" and "a mysterious and hilarious pic".

"[11] Mick LaSalle of the San Francisco Chronicle stated that "at its length, Biosphere is soporific and repetitive and puts viewers in the position of always being two steps ahead of it.