Mexican Lamprey

The Mexican lamprey (Tetrapleurodon spadiceus) is a jawless fish endemic to freshwater river systems of the central Mexican highlands, including the Lerma River basin. It is notable as one of the southernmost-occurring lamprey species in North America, in a region where lampreys are otherwise uncommon. The species belongs to the family Petromyzontidae and, like other lampreys, lacks true jaws, a bony vertebral skeleton, and paired fins, using a circular toothed sucking disc to feed as an adult. It spends the majority of its multi-year life cycle as a burrowing larva in river sediment before transforming into a free-swimming adult. Habitat alteration and water diversion in the highland rivers of central Mexico have raised conservation concerns for the species.

• Slender, scaleless, eel-like body, brownish to olive in color
• Circular sucking-disc mouth lined with rows of small, pointed teeth
• Seven round gill openings positioned behind the head
• Low, continuous dorsal fin extending toward a rounded tail
• Adult length typically 20-40 cm

The Mexican lamprey is distinguished from other freshwater fish sharing its highland rivers by its complete lack of jaws and paired fins, its scaleless eel-like body, and its circular sucker mouth, features not found in the bony fish species native to the same watersheds.

Mexican lampreys are restricted to freshwater river and stream systems of the central Mexican highlands, particularly within the Lerma River basin at relatively high elevation. They favor clear, flowing water with gravel or rocky riffle habitat for spawning, while larvae burrow into softer sand and silt deposits in slower-moving sections of the same rivers. As one of the few lamprey species adapted to subtropical highland conditions, the species has a naturally limited distribution. Water diversion, damming, and habitat degradation within its restricted highland range have reduced suitable habitat, making the species a subject of regional conservation concern.

Adult Mexican lampreys are believed to be parasitic, attaching to other fish with their toothed sucking disc and feeding on blood and body fluids for a period before releasing their host. As with other lampreys, feeding stops once the spawning migration begins, with adults relying on stored energy reserves to reach upstream gravel riffles, where they build a simple nest, spawn, and die shortly afterward. Larvae are burrowing filter feeders, straining algae, detritus, and microorganisms from river sediment for several years before undergoing metamorphosis into the adult form. The species plays a role in nutrient cycling within the highland river systems of central Mexico that it calls home.