Fish

Freshwater Fishes

The freshwater fish fauna of the LRGV reflects its combined northern, southern, and marine heritage. Tropical representatives including Mexican Tetra and Rio Grande Cichlid swim alongside northern fishes such as Buffalofish and Freshwater Drum. Sharing the waters with them are estuarine species that venture inland such as Striped Mullet, American Eel, and Gizzard Shad. Furthermore, introduced Old World species such as Common Carp and Blue Tilapia contribute to the LRGV’s ichthyological diversity.

Threats to the LRGV’s fishes include overfishing, damage or death from contact with power turbines and poisoning from industrial pollution and pesticide or herbicide runoff. Elsewhere, tropical predators such as Oscar (Astronotus ocellatus) and Peacock Bass (Cichla ocellaris) have escaped the pet trade and become threats to native fishes. Wherever such species are raised outdoors in shallow pools, there is always a risk of accidental dissemination during high water events. Of considerable importance to many species are the agricultural demands on the Rio Grande’s waters. Irrigation results in reduced river flows, which in turn raise water temperatures, lower oxygen concentrations, and strand fishes in isolated pools or channels where they are subject to increased avian predation as well as death from desiccation.

Amphibians

With the worldwide decline in amphibians, the 21 species that breed in the LRGV are of particular importance. Although depauperate in salamanders (their Texas population center lies in the Hill Country), the LRGV supports more than its share of frogs and toads. These 18 frogs and toads account for 25% of all the species of these animals known in North America. Additionally, one peripheral species is likely to be found on private lands in western Starr County. One species, the White-Lipped Frog is endangered in Texas, and three additional species are threatened: Mexican Treefrog, Sheep Frog, and Mexican Burrowing Toad. Two LRGV salamanders are endangered in Texas: The Black-spotted Newt, and the Rio Grande Lesser Siren. Unusual LRGV amphibians include:

o Giant Toad o Mexican Treefrog o White-lipped Frog o Rio Grande Chirping Frog o Sheep Frog o Mexican Burrowing Frog o Black-spotted Newt o Rio Grande Lesser Siren.

The continued existence of these water dependent species is inextricably linked to wetland habitats (such as resacas) and availability of wet areas.

Reptiles

Turtles

The 11 species presented in represent approximately 30% of Texas’ 35 turtle species and forms. Half of them are recognized by federal and/or state wildlife agencies as being either threatened or endangered. Turtles of concern in the LRGV include five marine species (Loggerhead, Common Green, Hawksbill, Kemp’s Ridley, and Leatherback), all persecuted for their meat and shells, and the Texas Tortoise, long a prize of the (now illegal) pet trade. Although sea turtles are protected in the U.S. and a few other countries, numbers are still taken for food or drown in shrimp nets. Additionally, their nesting beaches are subject to disturbance by natives and tourists, as well as development as resort communities.

Crocodilians

The only crocodilian occurring naturally in the LRGV is the American Alligator. The Spectacled Caiman (Caiman crocodilus) is occasionally seen in Texas, the result of introduction through the pet trade.

Lizards

Of the 50 species (64 forms) of lizards that occur in Texas, 13 occur in the Rio Grande Delta, with an additional 8 species occurring peripherally in Starr County. Two additional species have been introduced through the pet trade to the LRGV. The lizard population includes interesting species such as the Keeled Earless Lizard, Mesquite Lizard, Rosebelly Lizard, Four-lined Skink, and Laredo Striped Whiptail.

Snakes (Serpentes)

Thirty-three species of snakes occur in the LRGV, including several that are limited in the United States to these four counties. This represents approximately 40% of the Texas snake fauna. Two species are peripheral (and most likely would be found on private lands in western Starr County), and one has been introduced from Florida. Species of concern include Ruthven’s Whipsnake, Mexican Racer, Northern Speckled Racer, Texas Indigo Snake, Black-striped Snake, Northern Cat-eyed Snake, and Texas Scarlet Snake.

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