In 1978 to 1983 when doing exploratory rivers as a young river guide in Costa Rica, I came across an unusual fish in the mountains on the Atlantic Side of the country. I consider myself a keen observer of nature and a very good birder, but I know little of fish (my only fish studies was a college Marine biology course)and I have always wondered about this unusual fish and its behavior. I think I have determined it was some sort of Goby (Cling fish) but I'm not sure. One February, I came across a small dead fish in the Rio Chirripo Alantico, at between 3000-4000ft elevation, it is a fast moving river with lots of large rapids. This fish was about 5 inches long, mostly tan, but had some bright blue markings, very smooth skinned and had a large mouth (which at the time I recognized as Goby like), but most unusual was the suction cup on the ventral side where the pectoral fins met.
The next year, about a month earlier, I was exploring the river to the north, called the Rio Pacuare. I was at a somewhat lower elevation, but still a clear, fast moving rocky river with large rapids, we were camped below a large cataract and I noticed large schools of minnow sized fish (1-2 inches) moving determinedly upstream. There were millions of these small brown fish and they appeared to be a smaller version of the dead fish I had found the year before, except no blue color. There were two nonstop lines (both morning and through the night) of these tiny fish, with the smallest fish very near the shore, in water about 4-12 inches deep and another line of the larger fish (the 2 inchers) in water about 2 feet deep. There were lines of fish on both sides of the river. Once they got to the large volcanic boulders that formed the rapid they would swim (more like swarm) up in mass over boulders near shore, which had intermittent and varying flows of water over them, the elevation the fish had to go up in this rapid was at least 20 feet and the boulders were jumbled, many with vertical faces, that the fish were climbing. Many of the individual boulders they clung to had approximately 5 foot vertical faces. When the surge of water over a boulder backed off they would tenatiously cling to the rock face and each other, with their suction cups on their bellies, in mass groups entirely covering the rock in places, many losing grip and falling back into the torrent. The ones left on the rock face would hold very still and wait. When another surge of of water came over the rocks the fish would in mass swim like mad up the face and the rocks would appear to be wiggling. The optimum surge appeared to be 1-3 inches of water. I spent hours that evening and the next morning observing them and scooping up handfuls of these little fish that were filling the small pockets of water beneath these boulders and catch the ones falling back in my cupped hands and move them above their obstacles. The tiny pools of water just below the most difficult boulders were brimming with these little guys, more fish than water in some cases, as they all jostled and squirmed to get in position to make the leap up the boulder while awaiting the next water surge. This was a fascinating moment in my life and I have always wondered if anyone else has ever seen this?
Hiking at Havasu Canyon on a Grand Canyon River trip is almost a guarantee on every trip, motor or oar, but hiking to Mooney Falls, an 11 mile round trip hike is certainly not. On my last river trip, my 149th, we had 21 people do the hike. A record, there are only a handful of times that I have even seen this as a hiking option at Havasu. We had to camp close to Havasu Canyon and afterward camped early to pull this spectacular hike off!
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