To compare constant voltage and field inversion gel electrophoresis (FIGE) methods for detecting DNA strand breakage, two sets of DNA samples from freshwater bivalves were electrophoresed on both gel types. The first sample group contained DNA from mapleleaf mussels (Quadrula quadrula) exposed to lead; the second sample group contained DNA from Asiatic clams (Corbicula fluminea) that was passed through a syringe to physically induce strand breakage. A series of comparisons revealed that FIGE separated DNA into a greater number of bands, had less DNA in the band with the highest relative quantity of DNA, and resulted in a higher calculated average DNA strand length. The periodic inversion of the electric field on FIGE gels resulted in more complete separation of DNA fragments of different sizes, making FIGE the better of the two methods. Thorough separation of DNA fragments is a very important factor in the accurate calculation of average DNA strand lengths. Correctly determined DNA strand lengths are inte...