• Scientists have discovered two new-to-science species of fresh water fish on the Philippine island of Palawan.
  • A chance encounter at a waterfall revealed two types of goby fish.
  • But the researchers believe the fish may be at risk of extinction because of land disruption close to the area.

Serendipity underlies some of the greatest scientific discoveries. And it was certainly at play in 2015 when a team of biologists stopped off to relax at a popular waterfall on the Philippine island of Palawan after spending a long day surveying nearby streams to document the island’s freshwater fish diversity. Out of curiosity, they investigated what lived in the cool waters beneath the scenic falls, only to find a species of fish unmistakably new to science.

“I was very surprised,” Ken Maeda, a member of the survey team and staff scientist at the Okinawa Institute of Science and Technology (OIST), told Mongabay. He said the fish they found at Estrella Falls clearly resembled a genus of goby typically only known from temperate or subtropical parts of Asia. Finding it in tropical Palawan was “very unexpected,” let alone at such a busy spot where it had been flitting between the feet of swimmers, hidden in plain sight.

Maeda and his colleagues conducted subsequent investigations to confirm that the goby was indeed new to science. In the process, they found a second new goby species in the Cayulo River, a small stream on the opposite side of the island. The two new species, the Estrella goby (Rhinogobius estrellae) and Tandikan goby (Rhinogobius tandikan), which occur only in Palawan, were recently described and classified in the journal Zootaxa.

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The Tandikan goby (Rhinobogius tandikan)
The two discovered species are less than 5cm long.
Image: Mongabay/Ken Maeda

The two new-to-science species are completely isolated from one another. The Estrella goby is confined to a small stretch of river below Estrella Falls, where a steep stream flows from Mount Victoria into the main channel of the Malatgao River before flowing eastward into the Sulu Sea. On the other side of the island, the Tandikan goby lives in the 4-kilometer (2.5-mile) Cayulo River, which runs into the South China Sea to the west.

By analyzing mitochondrial DNA and assessing physical characteristics, the researchers placed both species in the genus Rhinogobius, of which there are currently more than 60 known species. Within the genus, they belong to an ancient lineage that was previously occupied by a single widespread species found from Japan to Vietnam. The two new Philippine species share certain attributes with this close relative, such as the arrangement of tiny sensory bumps on their cheeks, but they diverge sufficiently in other aspects to warrant classification as separate species.

The fish themselves are minute, measuring no more than 4.5 centimeters (1.8 inches) from snout to tail. They are nonetheless exquisitely patterned, sporting scores of electric-blue spots along their bodies — a feature that inspired Maeda to name one of the species after the brightly plumaged Palawan peacock-pheasant (Polyplectron napoleonis), known locally as tandikan.

A stream in Palawan
The only known habitat of the Tandikan goby is a small stream that runs into an estuary on the west coast of Palawan.
Image: Mongabay/Ken Maeda

In addition to describing the new species, the researchers were able to glean insights into their behavior. All of the Tandikan gobies the researchers examined had badly damaged tails and fins, and the males in particular appeared skinny and tattered. The study posits that despite their tiny size, Tandikan gobies could be aggressively territorial.

While the researchers have yet to assess the conservation status of the two new fish in accordance with IUCN Red List criteria, the fact that they are each only found in one small location heightens their extinction risk.

“Their endemic nature really raises the risk and threat level for both species,” Maeda said. “Any disruption to their habitat, such as dams, roads, leisure facilities or development of the land for agriculture could quickly lead to their extinction.”

And such disturbances could be imminent, according to Herminie Palla, study co-author and dean of fisheries and aquatic sciences at Western Philippines University. “Recently, the Philippine President has lifted the mining ban in the Philippines which gives way to five mining companies to operate in southern Palawan,” Palla told Mongabay in an email. One of the mining sites “is closely located [to] Estrella Falls.”