Abstract：Size and nucleotide polymorphisms of intron 1 of chemokine gene SCYA113 were studied in 60 individuals from 3 populations of channel catfish (Ictalurus Punctatus) with DPAGE and DNA sequencing. Results showed that there were 15 haplotypes and 8 length variants (from A to H), ranging from 395 to 443 bp. Sequence analysis of the 8 length variants showed the average composition of nucleotides (A, G, T and C) were 30.01%, 15.43%, 38.37% and 16.19%, respectively, and the GC content (31.62%) was much lower than that of AT content (68.38%). The GT/AG domain was found in exon-intron junctions,which was the 5′ and 3′ splice donor and acceptor sites in higher eukaryotic gene introns. Length variation was mainly due to the variable number of microsatellite TTC and TTA repeats. There were only 6 substitution sites excluding microsatellites: 3 transversions at 266 (T→A), 289 (G→T), 387 (G→C) and 3 transitions at 118 (C→T), 209 (G→A) and 250 (T→C), respectively. And the nucleotide diversity (π) was only 0.004, average number of nucleotide differences (K) was 1.576. The three populations have displayed the genetic diversity. In the P1984 population, eight length types and fourteen genotypes were observed. Eight length types and ten genotypes presented in the P1997 population. In the P2004 population, there were six length types and ten genotypes, and no allele A and B were found. Twenty-two genotypes are found from 60 individuals. All the genotypes are emerging at a lower frequencies (from 0.017 to 0.150), indicating the genetic resources is abundant.
