Comparison of the Fecal Microbiota from Long-term Captive and Newly Captured Whale Sharks (<i>Rhincodon typus</i>)

Despite its ecological importance, the gut microbiota of whale sharks (Rhincodon typus) remains poorly understood. Therefore, the present study exami-ned how environmental differences affect the fecal microbiota by comparing long-term captive and newly captured individuals. Fecal samples were collected over time from four long-term captive and two newly captured whale sharks, with seawater also being sampled from their respective tanks. Using 16S rRNA sequencing, 12,497 amplicon sequence variants (ASVs) were identified, including 6,976 classified as major ASVs. There were no significant differences in alpha diversity indexes between long-term captive and newly captured sharks; however, the latter showed slightly larger variance in four indexes. The ASV count per individual was slightly lower in long-term captive sharks than in their newly captured counterparts. In long-term captive individuals, Photobacterium was highly abundant. Conversely, Ureaplasma was dominant in newly captured individuals, but was barely detected in long-term captive sharks. Although alpha diversity did not differ significantly between the groups, a beta diversity ana-lysis showed clear distinctions. The high abundance of Ureaplasma in newly captured sharks suggests its involvement in nitrogen metabolism, possibly through urea recycling. Although further research is needed to clarify the taxonomic position and ecological functions of these Ureaplasma populations, the present study provides key insights for the conservation of wild whale sharks and improving health management for captive individuals.