Intestinal colonization patterns and growth modes of zebrafish symbionts. (A) Cartoon diagram of a 5-day-old larval zebrafish. The purple dashed box outlines the region imaged in panel C. (B) Diagram showing the boundaries of the bulb, midgut, and distal gut within the larval intestine. The estimated bulb-to-midgut boundary is located where the bulb begins to become patently narrow. The midgut-to-distal-gut boundary is approximately located where intestinal epithelial cells begin transitioning to a more colonic epithelial cell type (59). (C) Three maximum intensity projections of three-dimensional (3D) image stacks acquired by light sheet fluorescence microscopy for the indicated bacterial strains. An orange dotted outline marks the intestine in each image. Scale bar: 200 μm.