Complete nucleotide sequence of the cytochrome b gene of channel catfish Ictalurus punctatus and comparison of sequence homology among channel catfish and other fishes.

To clarify the phylogenic relationship of channel catfish with other fishes, the cytochrome b (Cyt b) gene of the catfish was cloned and sequenced. Channel catfish (Ictalurus punctatus) belonging to the family Ictaluridae in the order Siluriformes showed a 78.4-87.4% similarity to all but one fish of the family Cyprinidae and river loach Crossostoma lacustre of the family Balitoridae in the order Cypriniformes in which genes had already been sequenced, and a 97.2% similarity to the goldfish (Carassius auratus) belonging to the family Cyprinidae. Within the family Cyprinidae, a 78.8-89.2% similarity to one another was recorded. In addition, the similarity rate between the family Cyprinidae and the family Balitoridae reached a value of 77.8-79.9% in the order Cypriniformes. Furthermore, in an unrooted phylogenetic tree consisting of four branches among eight fishes, channel catfish and goldfish appeared in the same branch. These results suggested that the Cyt b gene of the channel catfish in the order Siluriformes was closely related to that of a goldfish in the order Cypriniformes. The results were not agreement with the morphological classification. Genetic reclassification of the fishes may be necessary to identify the ancestor. This is the first report on the cloning and complete sequencing the Cyt b gene of the channel catfish which may contribute to the genetic reclassification of catfishes belonging to the order Siluriformes.