Abbreviations: zebrafish into mouse, CONV-R zebrafish compared to Z-mouse microbiotas; mouse into zebrafish, CONV-R mouse compared to M-zebrafish microbiotas; zebrafish into zebrafish, CONV-R zebrafish compared to Z-zebrafish microbiotas (data from Rawls et al., 2004); mouse into mouse, CONV-R mouse compared to M-mouse microbiotas (data from Bäckhed et al., 2004). Similarity indices range from 0 (no overlap in composition) to 1 (identical communities).