The zebrafish zygote contains a large yolk cell which is absorbed over the first 5 days of life and supplies the developing embryo with nutrients. The yolk consists of a lipid and protein rich core with a cellular syncytium at its periphery, called the yolk syncytial layer (YSL). The YSL exports amino acids, hydrolyzes complex lipids to release fatty acids, and synthesizes lipoproteins, which export lipid to the developing embryo until it is able to feed independently (10). The intestine of the larval zebrafish is open at both ends and ready to absorb exogenous food at 5 dpf, though the non-enterocyte secretory cell populations do not differentiate until later larval stages (11). Once the intestinal tract is open, the gut microbiota are acquired from the media. At this time, colonization occurs essentially immediately and is maintained throughout life with the main source of variation in bacterial community composition being changes in diet (12).