Hawaiian gobies suck to climb waterfalls

Young Hawaiian goby fish are able to climb waterfalls using  a remarkable adaptation related to their feeding mechanism.

A new study on the `o`opu nōpili, one of Hawai`i’s five freshwater gobies, reviews the adaptation under the impenetrable title, “Evolutionary Novelty versus Exaptation: Oral Kinematics in Feeding versus Climbing in the Waterfall-Climbing Hawaiian Goby Sicyopterus stimpsoni.”

The authors are Heiko Schoenfuss of Saint Cloud State University in Minnesota and Joshua Cullen, Takashe Maie and Richard Blob of Clemson University in South Carolina.

They note that species that live in extreme habitats—like the steep, rugged, rocky Hawaiian streams with their tendency to flash flooding—often develop specialized traits to handle those conditions.

In the case of the nōpili, also called the rockclimbing goby, they adapted existing physical features to new uses. An oral sucker used to scrape algae off rocks for food, in the nopili’s case, is also used to help them “inch” up waterfalls.

Like other gobies, fused ventral fins provide them with a belly-side sucker that helps them cling to rocks. But the nōpili has something more. Instead of having a mouth that faces forward like many fish, the nōpili mouth faces down, and when traveling, it uses that mouth to hold on to the surface.

Is it a feeding mechanism adapted for climbing waterfalls, or a waterfall climbing feature that also happens to help the animal feed? That’s not clear, but it is clear that the downward-facing, sucking mouth gives the nōpili a nice advantage. And it is different from the other Hawaiian gobies.

While the others tend to suck their food off the rocks, the nōpili’s unique mouth allows it to scrape the algae. That means it eats a somewhat different diet from the others—that it has its own ecological niche.

It also lets it get to unique places:

“The oral sucker facilitates use of a novel mechanism for accessing upstream habitats above waterfalls. This form of locomotion has been termed ‘inching’ and requires alternate attachment of oral and pelvic discs to the rocky substrate, providing a slow, but steady, method of climbing that, in the Hawaiian species S. stimpsoni, allows individual fish to scale waterfalls up to 100 m tall,” the authors write.

For more on the `o`opu nōpili, the state Department of Land and Natural Resources has a page on the anatomy of the nōpili here. 

Here is a University of Hawai`i website with some images of the Hawaiian gobies.

© Jan TenBruggencate 2013