While up in Mexico last week (December 2001) I managed to make a stop at a cenote just outside of Chichen Itza in Yucatan State. A cenote is formed when the earth above an underground river collapses and creates a sinkhole. Cenotes are common in southern Mexico because the large number of underground rivers and the limestone base provide for unstable ground. The cenote I explored was located at Ik Kil in Xcalacoop, Tinum about 30 minutes from the ruins of Chichen Itza. Above ground, the cenote looked like a huge hole about 100 feet across. The water was about 150 feet straight down from the opening.
Descending into the cenote was very exciting. From the bottom looking 150 feet up (that is 15 stories!), what had looked like a huge hole while up top now looked like a small circle of light. After reaching the bottom, I could see hundreds of catfish in the water. The property owners plan to construct a tourism attraction at the cenote and had installed underwater pool lights just below the surface. The catfish were pure black and stayed near the water's surface. My first thought was that they were Hemibagrus! I thought that maybe someone had released Asian catfish into the cenote because these fish look just like black Hemibagrus. Only after swimming right up to the catfishes with my mask and snorkel and carefully counting the barbels was I sure they were not bagrids. They showed no fear of me probably because there are no predators, or even other fishes, in their natural environment.
I would guess that the catfish all stayed near the surface because they feed on whatever insects or animals fall into the cenote. Although now considered a junior synonym of Rhamdia laticauda, Barbour and Cole originally described these fish as R. sacrificii in 1906. Barbour and Cole chose the specific name as reference to the catfish's habitat in a sacrificial cenote near Chichen Itza. The ancient Maya would offer sacrifices of humans and treasure to the gods by throwing them into a cenote.
The water was cool at about 70°F, very deep, and crystal clear. Given the limestone nature of the cenote, I would expect the water to be rather hard with a pH of over 7. The largest specimens were about six inches total length. Given its attractive appearance and small adult size, it would make a very interesting aquarium resident. The tank could be aquascaped with limestone and lit by a blue or red tube. I am very curious as to how they reproduce as scattered eggs would sink perhaps a hundred feet deep or could be carried by the underground river to the sea. Also, because of their strange underground environment, they are not subject to the climatic or chemical changes that typically serve as spawning triggers. Given the large range of sizes that I saw, I believe this fish may reproduce year round.
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