The chromosome characteristics of red drum (Sciaenops ocellatus
) were analyzed to enhance the cytogenetic markers in Sciaenops ocellatus
by fluorescence in situ
hybridization (FISH) with 18S rDNA, 5S rDNA and telomeric repetitive DNA as probes. The karyotype of red drum consists of 48 telomeric chromosomes. FISH with 18S rDNA probes showed a single pair of signals at the secondary constriction sites of Chromosome 1. Whereas, two pairs of signal with different intensity were detected with the 5S rDNA probes: the strong signals were on the proximal of Chromosome 8, and the weak ones were on the interstitial of Chromosome 3. The signals of telomeric repetitive DNA appeared at both ends of all chromosomes with uneven intensity, and signals at the centromeric ended stronger than those at the distal ends, which facilitated determining the direction of the chromosome. These results, together with the available cytogenetic data of other sciaenids, suggested that the karyotype of 2n=48t and single 18S rDNA locus were the symplesiomorphic cytogenetic features of sciaenids, and the active and cryptic chromosomal rearrangements may have occurred along the evolution of sciaenids. The distribution patterns of these three kinds of repetitive DNAs would be useful to assist identifying the chromosomes of red drum, and be the basic data for studying chromosome evolution in Sciaenidae.