Never eat fish in or from a tank especially in a Chinese food restaurant, or for that matter any restaurant that boasts fresh fish and maintains tanks.
I am not sure if you know, but water dispersible liquids are commonly used to sedate these fish. Okay, I get it, we harvest fish in the wild, transport them sedated, then eat them. While you sedate your fish, (haha) be sure to buy from Aqui-s a the spiking tool: http://www.aqui-s.com/index.php/aqui-s-products/iki-jime
But seriously for those that adore “koi” they are often transported in containers by using anesthesia. The most common type is clove oil, which varies from lot to lot in the strength and composition. The major active ingredient is 90% Eugenol and it has been widely utilized for years. It is inexpensive and readily available without a prescription.