Freshwater Pufferfish in Belitung Uncovers Traces of Ancient River Lost Since Ice Age

Suhandi paddles his sampan through the dense mangrove plants in Tebat Rasau, a vast swamp in Lintang Village, Belitung Timur Regency. As he checked his fish traps, one pufferfish caught his attention: it immediately puffed up when held. “This is what we’ve been looking for; it’s safe to handle and consume because it’s non-toxic, unlike common pufferfish,” he said. For Suhandi and the people of Lintang Village, this fish has long been part of their daily lives, cooked for personal consumption, and its rough skin used for sanding sampans. But for scientists, this freshwater pufferfish holds something much bigger: biological evidence of an ancient river that flowed millions of years ago, connecting Belitung with Kalimantan long before these two regions were separated by the sea. According to the journal by Keim et al. (2021), freshwater pufferfish of the genus Pao are distributed from the Mekong River valley in Indochina to Sumatra. In the freshwater bodies of western Indonesia, four species have been identified: P. bergii in West Kalimantan, P. hilgendorfii in East Kalimantan, P. leiurus from Thailand to Java, and P. palembangensis in tributaries of the Musi River, Palembang. Of these four, only P. bergii and P. hilgendorfii are non-toxic and safe for consumption. Surprisingly, the species in Tebat Rasau is more similar to P. hilgendorfii from East Kalimantan, not to P. bergii from West Kalimantan, which is geographically much closer to Belitung. “The freshwater pufferfish in Tebat Rasau has very similar morphology and predatory ethology to the East Kalimantan species, P. hilgendorfii,” the journal states. This similarity is evident in the elongated to oval body shape, the position of the eyes, and...