In waters as acidic as vinegar—at a pH of 4—a small, resilient fish known as the Malay combtail (Belontia hasselti), meanders gracefully through the dark, tea-stained pools of the peat swamp forest. These waters are coloured by tannins released by decomposing organic matter. They are surrounded by a dense canopy of leaves and littered with the remains of fallen trees and leaves.