Assessment of negative phototaxis in long-term fasted Glyptocidaris crenularis： a new insight into measuring stress responses of sea urchins in aquaculture

A cost-effective method was designed to measure the behavioral response of negative phototaxis to high-intensity illumination in the sea urchin Glyptocidaris crenularis. Ninety sea urchins were randomly and equally divided into two aquaculture environment groups： a fasted group, which was starved during the experiment, and a fed group. After 10 months, the total mortality of each group was recorded. Then, 15 sea urchins were randomly selected from each group and behavioral responses to high-intensity illumination were investigated for each sea urchin. After the behavioral experiment, body measurements of the trial sea urchins were taken. The results reveal that food deprivation significantly affected test diameter （P〈0.01）, body weight （P〈0.01）, gonad weight （P〈0.0I）, and gut weight （P〈0.01）. Furthermore, food deprivation also affected negative phototaxis behaviors of time to rapid spine movement （P〈0.01）, time to the 1 cm position （P〈0.05）, and walking distance in 300 s （P〈0.01）, but not time to body reaction （P〉0.05）. The mortality rates of fasted and fed urchins were 6.7% and 0%, respectively. The present study provides evidence that food deprivation has a significant effect on phenotypic traits and behavioral responses to high-intensity illumination in the sea urchin G. crenularis. With this method, environmental stressors can be easily detected by measuring proper optional indicators. This study provides a new insight into measuring stress responses of sea urchins in aquaculture. However, further studies should be carried out to understand more environmental factors and to compare this potential behavioral method with immune, physiological, and epidemiological approaches.