Fig. 2

Richness and Shannon index mean values and standard deviations for the eight groups. Boxplot showing the richness (effective number of OTUs) (a) and Shannon index (b) values for the eight groups. The group name abbreviations are defined in Fig. 1. Groups of samples before formalin treatment are on the left side of the plot, while those after treatment are on the right. Gut content samples are colored in blue while gut mucosa samples are shown in red. Color intensity discriminates between healthy (light) and sick (darker). All groups show low alpha diversities. Statistically significant pairwise differences (Wilcoxon rank-sum test, p < 0.05) in the mean richness and Shannon index values among the groups are highlighted with an asterisk (*)