Abstract
A fragment of the cytochrome b gene was analysed by PCR/SSCP in Decapterus russelli samples from the Indo-Malay archipelago. Sequence analysis revealed two distinct mitochondrial clades (mean nucleotide divergence=2.2%) whose geographic distribution was heterogeneous (Nei's GST=0.416), pointing to a complex pattern of genetic differentiation and demonstrating limited genetic exchange between populations in this highly mobile species.