On the Issue of Statistically Significant Differences between the Average Values of Plastic Features in Two Groups of Juvenile Fish and between the Average Values of Their Indices

The regularities that determine the preservation and/or change of statistically significant differences during the transition from comparing the average values of plastic signs of juvenile fish to comparing the average values of their indices have been studied. An algorithm for evaluating the factors determining the variability of plastic features and their indices in allometry is proposed. Three cases of variability were identified and parametrized: (a) statistically significant differences are absent between the values of plastic features and their indices, (b) significant differences disappear when switching from comparing features to comparing their indices, and (c) significant differences in both cases remain. Case (b) is associated with different initial length of juveniles and different hatching time; case (c) is determined by different growth rates in the compared groups. The approach was tested on the selection of fingerlings of the Regsa fluviatilus L. perch from two reservoirs of the Staritsky district of the Tver region.