The objective of this study was to determine the fat and water-soluble vitamins contents (A, E, D, K, B1, B2, B6, B12, niacin, biotin, ascorbic, folic and pantethonic acids; in mg kg−1 fresh weight) lost during frozen storage (−24°C) in time intervals of 0, 1, 2, 3 and 4 months. Studied species included: Liza aurata (golden grey mullet), Cyprinus carpio (common carp), Clupeonella cultriventris caspia (common kilka or sprat), Rutilus frisii kutum (Caspian kutum) and Sander lucioperca (pike perch). Results showed that A, D and K vitamin losses occurred in all samples during storage, but no statistically significant differences were observed. Vitamin E losses under frozen conditions were significant in common kilka, Caspian kutum and pike perch, however, not in golden grey mullet or common carp. A decrease in vitamin C was significant in all fish species, but there were no significant decreases in other water-soluble vitamins (B1, B2, B6, B12, niacin, folic acid, pantothenic acid, biotin).