Experimental device and fish. A Experimental device. The test tank dimensions were as follows: height, 11.8 cm; width, 16.5 cm; and length, 29 cm. The internal divider had a length of 20 cm. The three zones of the experimental tank, i.e., the left zone, right zone, and neutral zone, are indicated. The position where the compounds were applied is indicated in red. B Morphology of paqr5b fish. Representative image of the head region and dissected ORs of the wild-type (paqr5b+/+) and mutant (paqr5b−/−) zebrafish. Scale bars are 1 mm for the head region (white) and 200 µm for the OR (black)

Behavioral analysis results of paqr5b after compound addition. The total time spent in three separate areas (left, neutral and right zones) after the addition of ATP (A), cadaverine (B), or DHP (C) is indicated. The results for the wild-type (paqr5b+/+) and mutant (paqr5b−/−) zebrafish are represented by open or closed bars, respectively. For each compound, 15 trials involving 5 fish of each sex were conducted. Each value represents the mean of the data, and the vertical lines indicate the standard deviation. The significant differences in the time spent in each zone between the wild type and the mutant zebrafish are indicated (**P ≤ 0.001, ***P ≤ 0.0001, ****P ≤ 0.00001)