A population of catfish presumptively identified as channel catfish (Ictalurus punctatus) found in Lake Maurepas in southeast Louisiana matures at a small size and early age (<170 mm TL and <2 years) compared to other populations in southern Louisiana (>500 mm TL and 3 to 4 years). In addition, these catfish have a protracted spawning period. The peak spawning time coincides with cultured channel catfish, but a percentage of the population spawns throughout the summer months. These fish are harvested at a small size and support an important but contentious commercial fishery. The small size and early age at sexual maturity have raised several questions: are these channel catfish, a distinct subspecies, or a hybrid between channel catfish and another ictalurid? These reproductive characteristics would prove useful for research, especially if the taxonomic uncertainty could be resolved. In this study, we differentiated these catfish by fin shape and external coloration from all other ictalurids present in Lake Maurepas except for channel catfish and blue catfish (Ictalurus furcatus). Blue catfish were differentiated by the absence of spots, anal fin shape and anal fin ray count. Genome size (cellular DNA content) determined for Lake Maurepas catfish in this study (2.11 ± 0.01 pg; N = 36) agreed with values for the Kansas strain of channel catfish (2.11 ± 0.01 pg; N = 15). Staining of chromosomes to determine the location (chromosome pair) of the nucleolar organizing region (NOR) revealed that the NOR for Lake Maurepas catfish did not differ from that of channel catfish. In addition, NOR for hybrids of Lake Maurepas catfish x blue catfish were located on heteromorphic chromosomes. A segment of an immunoglobin gene was sequenced from channel catfish, Lake Maurepas catfish, blue catfish, and black bullhead (Ictalurus melas). The nucleotide sequences for channel catfish and Lake Maurepas catfish were identical, while differences were found among the other catfishes. These data indicate the existence of a distinct population of channel catfish in Lake Maurepas that possesses traits useful for research.