Suckermouth Catfishes: Threats to Aquatic Ecosystems of the United States?

or “plecos” of South and Central America (Loricariidae) are markedly different from the bullhead catfishes of North America (Ictaluridae). Bullhead catfishes are terete and naked, with a terminal mouth and a spineless adipose fin. They are free-swimming predators that feed on invertebrates and other fishes. Suckermouth catfishes, in contrast, are flattened ventrally, their dorsal and lateral surfaces covered with rough, bony plates forming flexible armor (Fig. 1). Because of this armor, suckermouth catfishes are sometimes referred to as “mailed” catfishes (Norman, 1948). The mouth is inferior and the lips surrounding it form a sucking disc (Fig. 2). The adipose fin has a spine. The caudal fin is frequently longer ventrally than dorsally. Pectoral fins have thick, toothed spines which are used in male-tomale combat and locomotion (Walker, 1968). Suckermouth catfishes are benthic, adhering to streambeds and rocks with their mouths. They are vegetarians feeding on detritus and algae. Feeding is done by plowing along the substrate and using the thick-lipped, toothy mouth to scrape plant materials (filamentous algae, diatoms) from hard surfaces or to suck up fine sediments. Specimens in aquaria may live more than 10 years. Suckermouth catfishes are capable of breathing air by swallowing it and extracting oxygen through the gut lining (Norman, 1948). With more than 550 species, suckermouth catfishes constitute the largest family of catfishes in the world (Robins et al., 1991). Popular with home aquarists because of their distinctive appearance, hardiness, and propensity for cleaning algae from all submerged surfaces (including vascular plants), suckermouth catfishes have been commonly imported into the United States since the mid-20th century (Innes, 1948) and the number of taxa imported has increased during recent decades (Robins et al., 1991). Consequently, it is not easy, at present, to precisely identify specimens of suckermouth catfishes when they are found in U.S. waters. Taxonomy of this group has been described as “relatively primitive” and for some genera as “a mess” (Page and Burr, 1991; Armbruster, 2000). As a result, species-level identifications are tenuous. Forums exist for identifying specimens from photographs (e.g., http://www.planetcatfish.com) and some taxonomic resources are available on the Web, such as those for Loricariidae at the Auburn University Website (Armbruster, 2000), but comprehensive taxonomic keys to species are not yet readily available to resource managers. Also, taxonomists working with sucker-mouth catfishes are themselves divided into two different camps: “splitters,” principally Europeans, who divide the group into multiple genera and numerous species, and “lumpers,” principally Americans, who divide the group into fewer genera and fewer species.1 Confounding the problem of taxonomic resolution is the co-occurrence of multiple species in a single location and the possibility of interspecific hybridization. For example, three recognizably distinct forms occur at a single location in the San Antonio River in Texas (Fig. 1). These conform to characteristics of three of the species known to exist in the United States, but their close abundance and cooccurrence suggest the possibility of future hybridization.2 At present, American Currents Vol. 31, No. 3 1