A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was developed as a tool to prevent commercial frauds in fish products. The PCR was used to amplify the cytochrome b gene, part of the mitochondrial genome. The PCR products were digested with different restriction endonucleases (Alul, HaeIII, Hinfl, Hsp92, Taql) to identify five fish species - Mugil cephalus, Pomatomus saltator, Belone belone, Merlangius merlangus, and Oncorhynchus mykiss. None of the tested enzymes, alone, was able to distinguish between the five fish species, but by combining the results of two digestions, all five species could be differentiated. Thus, this method can be used to expose fraudulent substitutions with less valuable fish.