SUMMARY
Clarias macrocephalus Günther, 1864 is a Near Threatened freshwater catfish found in the Philippines and other Southeast Asian countries. Its numbers have dwindled over the past few years because of habitat loss and competition. This study examined the genetic diversity of the remaining viable populations of C. macrocephalus in the Philippines. Primers were designed to amplify via polymerase chain reaction (PCR) the complete mitochondrial DNA (mtDNA) control region (870-bp) in 120 specimens collected from three sites: (1) Buguey, Cagayan; (2) Camalaniugan, Cagayan; and (3) Agusan del Sur. Of the 120 sequences generated, only three haplotypes and two polymorphic sites were found. Overall haplotype and nucleotide diversity (h=0.479, p=0.00058) were alarmingly low, consistent with populations of other freshwater fishes that have experienced a genetic bottleneck. The overall FST value was 0.80050, indicative of large genetic differentiation between populations. The very low genetic variation found in all three C. macrocephalus populations calls for conservation and management efforts for the protection of the remaining populations of this economically important species.