Land-based aquaculture systems for fishes cause lots of stress. It is challenging to cultivate fish stably in such a condition, so we need stress-analyzing methods for fish. We have conducted experiments on flounders to give them high-temperature saltwater as a factor of stress cause and investigated the possibility of fast and easy fish stress analysis using Poincaré plot by calculating stress evaluation indexes such as RMSSD and sd2/sd1. As a result, we observed that flounders under a stress state come back to a relaxed state to weaken sympathetic nerve activity after giving the factor of stress cause as mentioned above.
