A method of identifying European freshwater fish species/lines in biological materials and fish products using the method of cleavage of the amplified S7-S7iCAPS intron polymorphic sequence based on the unique length of the JGM regions and/or specific restriction patterns of the partial genome sequence of the 1st intron of the S7 gene. The method consists in using a family or group-specific sets of primers, a unique combined variable length design of the JGM regions and/or InDel-CAPS and/or SNP-CAPS markers and is qualitative. A DNA sample from a biological material or a fish product is subjected to PCR analysis using species or group specific primer pairs defining a partial species/line specific sequence of the 1st intron of the S7 gene, called the J.G. Mendel (JGM) diagnostic region, wherein the JGM diagnostic regions are specifically defined for one species and have their specific length, whereupon identification of the species or hybrid is made based on the length of PCR products. After the PCR analysis i
