A new species of goby from the Philippines has just fallen

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  • Scientists recently described two new-to-science freshwater fish species from the Philippine island of Palawan: Rhinogobius estrellae and Rhinogobius tandikan.
  • The tiny blue-spotted fish are endemic to Palawan and each is confined to freshwater pools and streams in one location.
  • The fish were collected during surveys to document the diversity of freshwater fish on the island; both species belong to a genus previously known only from temperate and subtropical regions of Asia, with the new discovery extending its range south into the tropics.
  • Due to their restricted range, the fish are considered highly endangered and their habitats need safeguards against mining, road building and invasive species.

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

“I was very surprised,” Ken Maeda, a member of the investigation team and a 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 generally known only from temperate or subtropical regions of Asia. Finding it in tropical Palawan was “very unexpected”, let alone in such a busy place where it flew 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 species of goby in the Cayulo River, a small stream on the other side of the island. The two new species, the Estrella goby (Rhinogobius estrellae) and the Tandikan goby (Rhinogobius tantikan), which exist only in Palawan, were recently described and classified in the journal Zootaxa.

The Tandikan goby (Rhinobogius tantikan) is similar in size and shape to the Estrella goby, but has a yellow tint and appears to be more aggressive. Photo courtesy of Ken Maeda

The two species new to science are completely isolated from each other. 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 east into the Sulu Sea . On the other side of the island, the Tandikan goby lives in the 4-kilometre (2.5-mile) Cayulo River, which empties into the South China Sea to the west.

By analyzing mitochondrial DNA and evaluating physical characteristics, the researchers placed the two 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 Filipino species share some attributes with this close relative, such as the arrangement of tiny sensory bumps on their cheeks, but they diverge enough in other aspects to warrant classification as separate species.

The fish themselves are tiny, measuring no more than 4.5 centimeters (1.8 inches) from snout to tail. They are nonetheless exquisitely patterned, sporting dozens 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 (Napoleon wrasse polyplectron), known locally as tadikan.

The only known habitat of the Tandikan goby is a small stream that empties into an estuary on the west coast of Palawan. Photo courtesy of Ken Maeda

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

Although researchers have yet to assess the conservation status of the two new fish according to IUCN Red List criteria, the fact that they are each found in only a small location increases their risk of extinction.

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

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

Banner image: The Estrella goby, one of the new species of freshwater fish discovered in the Philippine island of Palawan, reaches 4.5 cm in length with orange fins and bright blue spots. Photo courtesy of Ken Maeda

Quote:

Maeda, K., Shinzato, C., Koyanagi, R., Kunishima, T., Kobayashi, H., Satoh, N. and Palla, HP (2021). Two new species of Rhinogobius (Gobiiformes: Oxudercidae) from Palawan, Philippines, with their phylogenetic placement. Zootaxa, 5068(1), 81-98. doi:10.11646/zootaxa.5068.1.3

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Animals, Biodiversity, Conservation, Endangered Species, Fish, Freshwater Fish, Habitat Degradation, New Discovery, New Species, Research, Rivers, Saving Species From Extinction, Species Discovery, Rivers tropical

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