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

We have studied the regularities that determine the preservation and/or change in statistically significant differences when switching from comparing the average values of plastic traits of juvenile fish to comparing the average values of their indices. An algorithm for evaluating the factors determining the variability of plastic traits and their indices in allometry has been proposed. We identified and parametrized three cases of variability: (a) statistically significant differences are absent between the values of plastic traits 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 Perca fluviatilus L. perch from two water bodies of the Staritsky district of Tver oblast. [ABSTRACT FROM AUTHOR]