Taxonomic name: Pylodictis olivaris (Rafinesque, 1818)
Synonyms: Hopladelus olivaris, Leptops olivaris, Opladelus olivaris, Pelodichthys olivaris, Silurus olivaris
Common names: mud cat (English), opelousas (English), shovelhead cat (English), yellow cat (English)
Organism type: fish
Pylodictis olivaris is one of the largest members of the catfish family and its introduction is the most biologically harmful of all fish introductions in North America as it predates heavily on native fish. Native to the warm water streams and rivers of the Mississippi River basin, it has been introduced east of the Appalachian Mountains and into several western states. P. olivaris prefers the slow moving water of large rivers and lakes and can be spread by unintentional stock contamination of channel catfish shipments, but in most cases, it has been intentionally stocked.
FWC (UNDATED) describes P. olivaris as having a flattened head, tiny eyes, a squarish tail and a protruding lower jaw that distinguishes P. olivaris from other catfish and contributes to it being placed in a genus of its own. This protuding lower jaw is an important characteristic when identifying the species (PFBC, 2003). They are yellow-brown and usually mottled above, with a creamy-white or yellow belly. P. olivaris can achieve weights of over 45kg but most weigh 1 to 7kg (FWC, UNDATED).
lakes, water courses
According to PFBC (2003), P. olivaris is found in large rivers, streams, and lakes, usually over hard bottoms. They prefer deep, sluggish pools, with logs and other submerged debris that can be used as cover. Young P. olivaris live in rocky or sandy runs in the river and in riffles.
Many feeding studies have found that Pylodictis olivaris prey heavily on sunfish (Lepomis spp.). One study also found that they reduced the number of common carp (Cyprinus carpio) and bullheads (Ameiurus spp.). However, the introduced population in the Flint River system was found to prey largely on crayfish, and it was also found that young-of-the-year P. olivaris fed on darters (Etheostoma spp.) clupeids, catostomids, ictalurids, and centrarchids. A severe decline in native fish species, particularly native bullhead species, was observed in the Cape Fear River within 15 years of the first P. olivaris introduction.
One ichthyologist believes that of all fish introductions in North America, introductions of flathead catfish, are possibly the most biologically harmful (Carter Gilbert., pers. comm., in Fuller 2000).
FWC (UNDATED) indicates that P. olivaris is highly regarded as a food fish when taken from clean water.
Native range: TPW (UNDATED) indicates that the native range of P. olivaris includes a broad area west of the Appalachian Mountains encompassing large rivers of the Mississippi, Missouri, and Ohio basins. Its native range extends as far north as North Dakota, as far west as New Mexico, and south to the Gulf including eastern Mexico.
Known introduced range: P. olivaris has been introduced east of the Appalachian Mountains and into several western states (Fuller, 2000). NatureServe (2002) reports that it also occurs in parts of Canada.
Introduction pathways to new locations
Other: The flathead catfish has been intentionally stocked in most cases (Fuller, 2000).
Local dispersal methods
Other (local): Pylodictis olivaris can be spread by stock contamination of channel catfish shipments (Fuller, 2000)
Preventative measures: The use of potentially invasive alien species for aquaculture and their accidental release/or escape can have negative impacts on native biodiversity and ecosystems. Hewitt et al, (2006) Alien Species in Aquaculture: Considerations for responsible use aims to first provide decision makers and managers with information on the existing international and regional regulations that address the use of alien species in aquaculture, either directly or indirectly; and three examples of national responses to this issue (Australia, New Zealand and Chile). The publication also provides recommendations for a ‘simple’ set of guidelines and principles for developing countries that can be applied at a regional or domestic level for the responsible management of Alien Species use in aquaculture development. These guidelines focus primarily on marine systems, however may equally be applied to freshwater.
Copp et al, (2005) Risk identification and assessment of non-native freshwater fishes presents a conceptual risk assessment approach for freshwater fish species that addresses the first two elements (hazard identification, hazard assessment) of the UK environmental risk strategy. The paper presents a few worked examples of assessments on species to facilitate discussion. The electronic Decision-support tools- Invasive-species identification tool kits that includes a freshwater and marine fish invasives scoring kit are made available on the Cefas (Centre for Environment, Fisheries & Aquaculture Science) page for free download (subject to Crown Copyright (2007-2008)).
Chemical: According to Sea Grant (2003), recent studies in Pennsylvania's Delaware Valley have been investigating P. olivaris physical and chemical sensitivities in hopes of finding a method of targeted removal, establishing selective barriers, or disrupting the spawning of the exotic species without harming native species. Researchers have discovered that P. olivaris exhibits a unique chemical sensitivity to the amino acid I-glutamine. After testing electrical responses of taste buds (or olfactory neurons) located on the skin and whiskers of the fish to 10 amino acids, it was determined that P. olivaris, unlike native channel catfish (Ictalurus punctatus), was most sensitive to I-glutamine.
FWC (UNDATED) states that P. olivaris is a predatory fish and will consume bass, bream, shad, crayfish and often feed on other catfish. The young rely more extensively on aquatic insects and crayfish than do the adults. They rarely eat dead or decaying matter.
According to FWC (UNDATED), spawning occurs in late spring when water temperatures reach 21 to 27 degrees celsius. One or both parents excavate a nest that is usually made in a natural cavity or near a large submerged object. Females lay a golden-yellow mass of up to 100,000 eggs. Males guard the nest and agitate the eggs to keep them clean and aerated. The young remain in a school near the nest for several days after hatching, but soon disperse.
Reviewed by: Rob Weller. Senior Fisheries Biologist Georgia Department of Natural Resources Wildlife Resources Division. USA.
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Monday, 24 January 2005