Computational analysis of movement behaviors of medaka (Oryzias latipes) in response to chemical and thermal stressors

Abstract

Response behaviors of medaka (Oryzias latipes) were computationally analyzed after exposure to a temperature increase and toxic treatments. The temperature was increased from 25 °C to 35 °C while individual organisms of medaka were treated with copper at a low concentration (1.0 mg/L). Movement tracks were continuously recorded for 6 hours before and for 6 hours after the treatments. Parameters (e.g., speed and stop number) and entropy values (e.g., Shannon entropy and Réyni entropy) characterizing the movement tracks were calculated before and after the treatments. After the temperature increase, parameters and entropy values remained in the same range. Test organisms appeared to adapt to a gradual temperature increase to maintain the same behavioral state. After the treatments with copper, however, parameters such as speed, acceleration and stop number substantially decreased while the turning rate increased. Entropy values such as Shannon and Réyni entropies were lower while Simpson index was higher after the chemical treatments. Complexity residing in the movement tracks appeared to decrease after the treatment with a chemical. According to the self-organizing map results, entropy values were associated with speed and acceleration. The parameter (speed) and the entropy value (Shannon entropy) changed in different time periods after the chemical treatment. The periodicity in entropy was not different between the early and the late periods after the treatments according to fast Fourier transform. The feasibility of computational monitoring and the structure property in the behavioral data were further discussed regarding ecological assessment of environmental stressors.