Characterizing response behavior of medaka (Oryzias latipes) under chemical stress based on self-organizing map and filtering by integration

• Complex behavioral response (BR) was outlined by SOM and filtering by integration
• BR modes were quantitatively confirmed based on integral behavioral strength (BS)
• Intoxicating and recovering tendencies were addressed by residual curves of BS
• Response landscapes would be suitable in establishing toxic referencing system

Behavioral responses (BRs) of medaka (Oryzias latipes) were observed after exposure to low concentrations (0.1 TU (Toxic Unit, TU), 1 TU, 5 TU, and 10 TU) of trichlorfon, parathion and malathion. Overall response patterns of test organisms were reflected from surface shapes of BS (Behavior Strength) values in 3-D: parathion appeared to be most variable in presenting response behaviors whereas trichlorfon showed relatively simple response patterns. The self-organizing map (SOM) addressed the time and toxic effects efficiently. An evident circadian rhythm observed in the control diminished at a low concentration of toxic unit, and variability of toxic effects was accordingly observed according to chemicals and concentrations. Subsequently filtering by integration was conducted to time series BS values. The highly fluctuating nature of original BS values was filtered efficiently to produce linear fitting closely. Slopes of regression decreased monotonically as toxic concentrations increased. Residual curves of integral BS values from linear fitting were further used for determining different BS phases proposed by empirical observations; the positive and negative phases were in accordance with acclimation, adjustment and toxic effects in behavior response modes. According to inclination and declination periods observed in residual curves, new states of test organisms were further defined to present intoxicating and recovering tendencies Profiles based on residual curves of integral BS values were able to show landscape of response patterns across toxic concentrations in different chemicals. Computational methods for defining behavior states provide an objective ground for analyzing complex stress response and could be suitable in referencing toxic behavior modes of test organisms quantitatively.