Baikal Research Centre 1 article published in JoVE Biology Simple and Effective Administration and Visualization of Microparticles in the Circulatory System of Small Fishes Using Kidney Injection Ekaterina Borvinskaya1,2, Anton Gurkov1,3, Ekaterina Shchapova1, Dmitry Karnaukhov1, Anton Sadovoy4, Igor Meglinski1,5, Maxim Timofeyev1 1Institute of Biology at Irkutsk State University, 2Institute of Biology at Karelian Research Centre of Russian Academy of Sciences, 3Baikal Research Centre, 4Institute of Materials Research and Engineering, Agency for Science, Technology, and Research (A*STAR), 5University of Oulu, Optoelectronics and Measurement Techniques Laboratory This article demonstrates the principles of a quick, minimally invasive injection of fluorescent microparticles into the circulatory system of small fishes and the in vivo visualization of the microparticles in fish blood.