The paper proposes an index that adds to characterisation of length growth in various fish species. The index, mean length increment ratio, describes the shape of the growth curve. The analyses included 799 samples (about ten to several hundred individuals in each sample) of 20 fish species. The mean increment ratios were determined in four methodological variants (A, B, C, and k); detailed statistical analysis, however, has revealed that the A variant, calculated using the full age range of the material, is the most authoritative one. The values of A ranged from 0.60 (herring) to 1.02 (wels). The mean A for 20 studied fishes was 0.89. The A value was found to be significantly correlated with age (for 17 out of 20 analysed fishes). Cluster analysis (performed for A and k) demonstrated that 3 species (herring, vendace, and whiting) were considerably distant from the remaining 17 species; those 3 fishes exhibited a sharp decrease in growth rate, which in the other species was more even.

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