Mould-like Deterioration of Anji Salamander (Hynobius amjiensis) Egg Capsules: Adverse Effects, Potential Pathogenic Factors, and Conservation Intervention

Fungal infection is a major cause of hatching failure in amphibian embryos. However, studies in Hynobiidae remain limited. Across four breeding seasons (10 November 2022–15 April 2026), we combined field monitoring of hatching rates and mould-affected egg proportions, lesion phenotyping, 18S and 16S rRNA gene sequencing, and a conservation intervention to characterise egg-capsule mould-like deterioration in the Anji salamander (Hynobius amjiensis), identify candidate pathogenic microorganisms, and evaluate the effect of the intervention on the survival rate of Hynobius amjiensis. The proportion of mould-affected eggs differed significantly among breeding seasons (2.05%, 4.02%, 8.24%, and 7.09%; p < 0.001), coinciding with reduced rainfall and higher temperatures during the same periods. White hypha-like growth accompanied embryonic necrosis in affected egg capsules; a few hatchlings showed developmental abnormalities. Eukaryotic and bacterial community compositions differed significantly among sample groups (18S: p = 0.010; 16S: p = 0.045). The relative abundances of Ascomycota, Zoopagomycota, and Basidiomycota were higher in affected embryos, and those of Chytridiomycota and Mucoromycota were higher in affected intestinal samples, but no bacterial taxon was consistently highly abundant. The intervention group had a significantly higher hatching rate (65.47% vs. 46.57%; p < 0.001) and a significantly lower malformation rate (5.48% vs. 12.66%; p < 0.001) than the natural-condition group. These findings can inform disease prevention and control in hynobiid salamanders and other amphibians.