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ABSTRACT Resistance and reactance of chilled, frozen-thawed and double frozen-thawed fillets of Atlantic chub mackerel ( Scomber colias) were measured in a frequency range from 0.1 to 1,000 kHz. After the measurements in the fresh state, one group of samples was slow frozen in a freezer set at temperature −20 ± 2C, while the second group was fast frozen by immersion in liquid nitrogen. After 14 days of frozen storage, the samples were thawed and electrical parameters were measured. The measurements were repeated on double frozen-thawed samples. Results showed that the reactance measured at frequencies higher than 150 kHz can distinguish fast frozen from slow frozen fillets. Obtained difference between freezing cycles measured with the reactance at low frequencies could have been influenced by electrode polarization and the consequence of the measuring setup. Overall findings are in accordance with the ones obtained on the farmed fish indicating that the reactance may point to the differences in a fish muscle structure caused by different freezing history. PRACTICAL APPLICATIONS This preliminary work is addressing the problem of varying quality of frozen fish fillets on the market today. Therefore, bioelectrical impedance measurements were used to monitor fish tissue properties after freezing under different conditions. Impedance measurements and especially reactance show the potential of detecting the differences among fillets with different freezing history. With further adjustments of the measuring setup and proving the advantage of this method over other spectroscopic techniques, this method may be used in a quality control of frozen fish. [ABSTRACT FROM AUTHOR]