Waterfall climbing fish

Diadromous fish are those that live part of their lives at sea and part of their lives if freshwater. Some of these fish reproduce in the upper parts of rivers above barriers like waterfalls, which they must scale in order to make it to the breeding sites. A newly published paper looks at how the Nopili goby, Sicyopterus stimpsoni, manages to climb waterfalls. The researchers found that the way the goby feeds and the way it climbs are very similar.

The Nopili goby, Sicyopterus stimpsoni (photo Takashi Maie)

During feeding the Nopili goby extends its upper jaw out much further and its lower jaw much less than other gobies. In climbing the basic motion is the same except the upper jaw maintains closer contact with the rock. Climbing is also assisted by pelvic fins fused into a sucker, a feature of all gobies. Because no other goby feeds in the same way, it's unclear whether the feeding or climbing movements evolved first.

The climbing galaxias, Galaxias brevipinnis (photo Robert McCormack)

There are many other fish that have a diadromous life-history, eels and salmon being the classic examples. There are fewer fish that climb waterfalls. However, in southern Australia and New Zealand there is a fish close to my heart that has a very similar life-history to the Nopili goby, but it climbs waterfalls in a different way. The climbing galaxias, Galaxias brevipinnis, climbs using its broad pectoral and pelvic fins and wiggling upwards.

Cullen J. A., Maie T., Schoenfuss H. L., & Blob R. W. (2013). Evolutionary Novelty versus Exaptation: Oral Kinematics in Feeding versus Climbing in the Waterfall-Climbing Hawaiian Goby Sicyopterus stimpsoni PLOS One, 8 (1) DOI: 10.1371/journal.pone.0053274