Defense Date


Document Type


Degree Name

Master of Science



First Advisor

Gregory C. Garman


Species introductions have been linked to the decline of native taxa, and in many cases have resulted in the elimination of native species in both terrestrial and aquatic systems throughout the United States. In aquatic systems, a particular threat is the introduction of large piscivorous fish that may alter the native fish community structure. For example, introductions of large ictalurids such as blue catfish, (lctalurus furcatus), and flathead catfish, (Pylodictus olivaris), into coastal Virginia rivers, including the James River twenty years ago have resulted in the establishment of these large, predatory fishes.

This study described the trophic ecology of four ictalurid catfishes in the tidal James River, Virginia including the native white catfish (Ameiurus catus), the possibly introduced channel catfish (Ictalurus punctatus), and the recently introduced blue catfish and flathead catfish. The objectives of this study were to determine the trophic ecology of these four catfishes in a coastal Virginia river, and to assess the potential predatory effects of large, recently introduced piscivorous ictalurids on the native fish assemblage, and especially anadromous clupeid fishes.

A stratified sample of 4, 164 catfish was taken throughout the tidal freshwater reach of the James River during the summer and fall, 1996 and spring, 1997. Stomach content analysis revealed that blue catfish and flathead catfish are highly piscivorous, feeding on several families of native fishes. Flathead catfish consumed over 90% (frequency of occurrence) fish prey in most predator size classes and began consuming more fish prey at smaller sizes than blue catfish. Blue catfish shifted to a mostly piscivorous diet at predator lengths > 500 mm. Both blue catfish and flathead catfish consumed adult anadromous clupeids. The greatest numeric proportion (0.41) of anadromous clupeids consumed were juvenile Alosa spp. (<100 mm) taken by small blue catfish (<500 mm) during the fall sampling season. Piscivory was much less extensive in channel catfish and white catfish (less than 10% frequency of occurrence for all predator size classes). There is evidence of negative consequences to native fishes associated with the introductions of blue catfish and flathead catfish into Atlantic slope rivers. These consequences may conflict with current restoration efforts for native fishes such as the anadromous clupeids in these rivers.


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