Guwahati: Researchers from the University of Delhi have discovered a frog with blue bones and green blood from Arunachal Pradesh in the Northeast region of India. This is the first Indian frog to exhibit this unique characteristic, which is known only in a handful of species in other parts of the world, including Southeast Asia and faraway regions in Madagascar and South America.
The findings have just been published in the journal Zootaxa. This new study also reports a new country record for another species that was previously known only from neighbouring regions of China.
The genus Gracixalus is a group of tree frogs in the family Rhacophoridae, currently comprising 16 species distributed across Asia. This group was recently reported from India and until now represented by a single species, Gracixalus patkaiensis (Patkai green tree frog). Not only do we now have another species in India, Gracixalus medogensis (Medog small tree frog), but also one of them with a mysterious trait.
India’s first frog with blue bones and green blood
The Patkai green tree frog was formally described from Namdapha National Park, India, in 2022. While studying this species, a team of researchers led by Professor S. D. Biju from the University of Delhi came across an additional exciting finding.
“Finding these tiny frogs in bamboo thickets, from where they make whistling calls, is not easy. Upon eventually locating one, we were amazed by the frog’s completely translucent body and externally visible blue bones and green blood. I had not seen such a frog anywhere in India, in over three decades of my work on Indian amphibians,” says Biju.
India is home to over 420 species of frogs, and the Patkai green tree frog is the only one known to show this characteristic. The occurrence of turquoise bones and green blood is also globally rare. Within Asia, species in only two tree frog genera are known to show this trait, including three other species in the genus Gracixalus (G. quangi, G. gracilipes, and G. supercornutus) from Vietnam, Laos, and southern China. Studies on similar South American frogs have looked at the biochemical basis and potential ecological significance of such a trait. It likely provides some evolutionary advantage to these frogs and that requires deeper investigations specifically in the case of this new finding from India.
This work was undertaken as part of one of Biju’s students, Tage Tajo’s, PhD research on amphibians of Arunachal Pradesh, a region harbouring many endemic species found nowhere else in the world.
Another Chinese species new to India
During field surveys in the Lower Subansiri and Lower Dibang Valley regions of Arunachal Pradesh, the team discovered two new populations of another species, the Medog small tree frog, scientifically known as Gracixalus medogensis. This species was originally described from the Medog region in Tibet, China, in 1984 based on a single specimen, and knowledge about it remained limited. The populations from Arunachal Pradesh constitute the first record of this species from India, confirmed based on their external appearance and similarities in DNA, as well as the first characterisation of the species’ unique whistling call.
Understanding species using multiple criteria expands our knowledge of their biology as well as conservation requirements. Such new findings further underscore that documenting and protecting India’s unique amphibian fauna needs to be a priority.
The study, titled “Whistles in the reeds: a new country record of the deeply divergent Gracixalus medogensis, with additional insights on Gracixalus frogs (Rhacophoridae) in India”, was published in the latest issue of the journal Zootaxa dated 7 July 2025 (link to article).
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