Mathematical modeling of preference intensity of Japanese Medaka Fish for instream water environment using fuzzy reasoning

Fish behavior is essentially vague, and the behavioral responses to an environmental change vary widely both among individuals and depending on circumstances. This suggests it is necessary to positively consider the uncertainty when constructing preference intensity models to environmental factors. In this paper, the essential vagueness of the behavioral responses of Japanese Medaka Fish (Oryzias latipes) was positively taken into consideration in studying the preference intensities of the fish to three environmental factors: water depth, current velocity, and cover. The factors were quantified by laboratory open-channel experiments and a fuzzy reasoning technique. The Japanese Medaka Fish, a river fish, was selected to quantify preference intensities because it has become symbolic of the restoration of the countryside ecosystem in Japan. A simple genetic algorithm was introduced to search for an optimal structure of a fuzzy preference intensity model. The fuzzy preference intensity model was then verified by on-the-spot examinations. The results indicated that the two environmental factors of current velocity and cover obviously affect the environmental preference of Japanese Medaka Fish, and the fuzzy preference intensity model was a reasonable model to account for the actual behavioral responses of the fish.