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The Mexican Tetra

Astyanax mexicanus (Filippi, 1853)

last updated 09 January, 2009

The Mexican Tetra (Sardina de Mexico) is a common open water species to the inland cenotes of Quintana Roo. This subtropical species is found in diverse aquatic habitats throughout Mexico, as it is able to thrive on a variety of food sources (including smaller fish, invertebrates, human phlegm, plants, and algae) while tolerating a liberal range of temperature conditions. A. mexicanus normally schools in large groups. Each individual can display aggressive tendencies when breeding or food opportunities are presented.

In the last decade this vertebrate has learned to exploit cave divers' lighting systems to follow explorers; it is a ruthless hunter of stygobitic populations within the cave environment. These ventures were limited at first to "round trip" feeding excursions. At this date it is not uncommon to find a handful of A. mexicanus loitering far within the cave zone, waiting for a new group of cave divers to illuminate additional prey or the means back to a cenote. This species of Tetra has decimated blind fish and invertebrate Crustacean populations in the Carwash, Sac Actun, and Naranjal caves. It appears that other underwater caves are beginning to suffer from matching circumstances. 

Mexican Tetra

Graphic: J. Sublette, 1990. The Fishes of New Mexico.

During the 2002 QRSS Convention, Dr. Tom Iliffe from Texas A&M University at Galveston presented a lecture on "Endangered Caves and Cave Animals of the Yucatan Peninsula". Dr. Iliffe addressed the increasing challenge of A. mexicanus, while proposing a community study on the frequency and effects of Tetra incursions into local caves. This study may help us reach a more complete understanding of the problem. Should you have direct experience with Tetras in an underwater cave and wish to participate in this effort, please follow the link below.

This link will take you to a page on the Cave Biology web site. Fill in the information requested and submit. Note that Netscape browsers may have difficulty in accessing this page.

As an update to this page, the Mexican Tetra survey (and Cave Biology pages) are difficult to access. This may reflect lingering problems with the Texas A&M University server from 2008 hurricane damage.

Updates and corrections are welcome: chac<at>consolidated.net

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