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Tuesday, September 18, 2012

Dive Laguna de Apoyo

Most tropical lakes have dark water, but a few, like Laguna de Apoyo, make for excellent SCUBA diving. This lake is sitting in a volcanic crater, formed 23,000 years ago. Our research group is busy here, studying the fishes of this lake, because something interesting happened during those years since the volcano left a huge hole in the ground, it filled with water, and the fish entered. Some of them transformed into new species, and they provide scientists with a great field location to consider how evolution occurs. We are responding to the call to study these fascinating fish, all evolved from Amphilophus citrinellus, the Midas cichlid.

Midas cichlid
Juvenile fishes leave their refuge to investigate divers in their area. Photo by Garey Knop.
Our group has discovered five new species in this group of fishes in Lake Apoyo. Adding to the list the arrow cichlid, Amphilophus zaliosus, discovered by Barlow and Munsey in 1976, and we have to date, a group of six closely related fishes with similar appearances, plus an unknown number of other fish that may also be recognized someday as unique species. Several of those fish are seen in the video below, taken by Garey Knop in one of our monitoring dives.

The fish of this special group are important for more reasons than just for having evolved recently into a rainbow of new species. The members of this species group provide very interesting parental care to their offspring, until the babies are several weeks old. We are very interested in how these special fish choose their mates, find their breeding grounds, and defend their fry. Here is another video by Garey Knop, in which a pair of arrow cichlids (Amphilophus zaliosus) are defending their fry, only three days since becoming free-swimming. The fry are difficult to see, but there are about 1200 of them, usually beneath the female (the smaller of the parents).
This breeding pair has made a nesting site in a featureless area, with filamentous algae covering the muddy/sandy substrate. The pair dug a hole about 80 cm wide to uncover a basalt rock surface where the eggs were deposited and fertilized. The nearest nest to this one was about ten meters away. Relatively few fish passed through the area, excepting the harmless Atherinella sardina (silversides). Both parents were busy, vigorously defending the fry. During our half hour watching the pair, the fry boldly approached us, and some of them fed on the skin on the photographer's hand! 

laguna de apoyo
Garey feels at home underwater. Lake Apoyo does not have dangerous fish or currents. Photo by Garey Knop.
Dive Nicaragua
Lots of blind fish are found in Lake Apoyo. A parasite is suspected, although the eyes are removed by other fishes once the fish go blind. The epidermis of this fish has covered the orbit after the eye was extracted. This fish has several slash marks caused by other fishes in their attempts to bite the eyes. Photo by Garey Knop.
This blind fish shows the eye clouded by cataract. The opposite eye had already been eaten by other fish. Note the caudal fin missing a large piece, presumably eaten by some predator. Photo by Garey Knop. 
laguna de apoyo
Crabs (Potamocarcinus nicaraguensis) are common in Lake Apoyo. Photo by Garey Knop.
In a typical monitoring dive, we see about a thousand fish. Almost every dive we see a crab.  From November through January, lots of fish are reproducing, and we can watch them provide parental care up close. Lake Apoyo has the clearest and cleanest water of any lake in Central America.

Dive Nicaragua
We gather data from the best perspective, watching the fish from a few meters distance. Photo by Garey Knop.
Would you like to help us study these fishes? If you are a certified open water diver, you can accompany our staff on a monitoring dive, and help us learn more about these fascinating fish to protect them better. Please let us know-we will take you on a dive.
scuba diving
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