ROCK-CLIMBING GOBIES

     Rock-climbing napili gobies are seven-inch, amphidromous fish that are another of innumerable miracles on Earth.  They hatch in stony-bottomed, clear-running, freshwater streams in Hawaii's forested mountains and slopes, but are soon swept over waterfalls by the current and on down to the Pacific Ocean where they live as juveniles and filter-feed on plankton for about six months.  Then swarms of them swim back to the mouths of their nursery waterways where, within two days, their mouths turn down and become suction-cup-like, and they each develop a suction cup on each enlarged, front fin.  Now those juvenile gobies are ready to ascend wet, slippery rock walls right beside and just behind waterfalls on their birth waterways.  And what an arduous climb it is, too.

     Alternately using their down-turned, sucker-like mouths and the suction cups on their front fins to create suction to adhere to the wet rocks, groups of them slowly inch up those rocks by waterfalls to the clear-running stream above where they hatched about six months before.  It might take up to three days to crawl up those slippery rocks.  And many of them don't reach the summit of the waterfalls, as the falling water sweeps them off the rocks.  But the gobies that do reach the streams above the waterfalls, strongly swim against the powerful current of those waterways and into calmer parts of them.  The dark-brown and beige-banded gobies are well-camouflaged on the rock walls and their streamlined bodies allow most of them to push against falling water and strong currents.     

     Adult Napili gobies mature in the mountain streams above the falls, and live up to five or six years in them.  They spawn on rocks on the bottoms of those waterways.  Male gobies develop blue and red colors to attract females to them for spawning.  Ocean fish can't eat the eggs or small young of gobies in mountain waterways above waterfalls, but there is little food for adult and hatchling gobies both.  However, the hatchlings are swept downstream and over the falls to the ocean where food is abundant: problem solved.    

     Mature gobies use their down-turned mouths to feed on alga clinging to rocks on the bottoms of the streams.  And herons and Sandwich Island sleepers, a kind of large gobie fish, in turn, are some of the creatures that prey on Napili gobies.

     Hawaii's mountains were caused by volcanos rising from ocean depths.  Napili gobies adapted to the torrents and falls that rush off the slopes to the Pacific Ocean.  They are successful in adjusting to a relatively safe niche above waterfalls.  They are an intriguing species in a beautiful habitat.     


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