Biological characteristics of rotifers under treatment (100 µM) with KYNA or its analogs showing contradictory profiles. On day six, three experimental- (number of rotifers alive (NRA), body size index (BSI), mastax contraction frequency (MCF)) and one chemical cellular reduction capacity (CRC) parameter of individual rotifers and the populations were monitored. KYNA (A) and its SZR analogs (B–E) had antagonistic profiles for the following characteristics: NRA-BSI compared to CRC-MCF pairs, with the exception of SZR109 (F). Both Philodina and Adineta species show significant differences from their untreated controls (showing as 0 value on the x axis in graphs). The error bars represent SEM. One-way ANOVA with Bonferroni post hoc test was used for statistical analysis, the levels of significance are * p ≤ 0.05, ** p ≤ 0.01 and *** p ≤ 0.001. (*, significant difference from untreated controls, where the corresponding data of 100% is the 0 value on the x axis); NRA, n = 24 wells; BSI, n = 50 randomly selected individuals from 24 wells; CRC, n = 24 wells; MCF, n = 50 randomly selected individuals from 24 wells).