On this day we hit the Rio Coloradito in search of Amphilophus lyonsi. We didn’t find any, nor many cichlids at all. The only two cichlids that we saw spawning was a pair of Tomocichla sieboldii and Astatheros altifrons.
As usual, the Rio Coloradito was full of tetras. Occasionally I’ve had leg and chest hairs ripped out by tetras when I snorkel and am not wearing a wet suit. Today, while wearing a wet suit the Tetras still decided to attack, and this meant ripping hairs out of my beard an mustache. The Rio Coloradito has lots of scale eating tetras. These guys make it hurt a bit more as they do a little turn when they rip out a hair.
The Rio Coloradito is interesting because here we begin to see some South American fish creep up into Central America. Here we begin to see different tetras, catfish, and we even start to see plecos.
The Rio Coloradito has a bunch of other fish as well. Today there were tons of gobies as well as Brachyraphis. There were also hundreds of shrimp in the river.
After the Coloradito, we headed to the Osa peninsula. Not much is known on the freshwater fish of this are as this are just got a road built. The one study that was done here was done on the other side of the peninsula. We explored the east side. The ride was more than a bit bumpy as the new road had lots of pot holes and in extreme cases, on lane had fallen down the cliffs at some areas. We entered the Rio Conte first and saw a very interesting tetra as well as mollies, gobies, and a bunch of Cryptoheros sajica.
Our next stop was the Rio Barigones. We saw here another breeding pair of Cryptoheros sajica.
What was even more amazing is our arival was timed with one of the coolest migration events I’ve ever seen. These rivers are full of Sicydium gobies (the Rio Barigones has Sicydium adelum in it). Sicydium gobies are amphidromous, meaning that they have part of their life cycle in the ocean and part in freshwater. Adult fish spawn in freshwater and guard their eggs. The eggs then hatch and the small larvae flow down river into the ocean where they drift with the plankton. These gobies develop into fry in the ocean and at about 1/2″- 1″ in length they migrate up to freshwater to mature and live their adult lives.
It was a rare occurrence by chance that we were able to see this event. The river was full of millions of gobies! They were so thick, it was like watching a river of gobies flow within the river. Many fish were loving this as they were able to get a quick goby snack. Here is some video of the migration. These videos really don’t do justice to the amount of fish in the river.
What a long day. We finally got back to the research station at 4 in the morning!