Japan exported about $600 million worth of aquatic products to China in 2022, making it the biggest market for Japanese exports, with Hong Kong second. Sales to China and Hong Kong accounted for 42% of all Japanese aquatic exports in 2022, according to government data.
Because the color gradient is relative. A large enough banana would also light up. Also exposure time is another factor and this will dissipate very quickly. You can play it safe by abstain of seafood and swimming for a week.