For the first time, the "Unidentified Blood Organism" (UBO) and the "Swimbladder Protozoan" (SBP), interpreted as the early stages of Sphaerospora in Europe, were recorded from common carp (Cyprinus carpic) on the China territory. Our studies suggest that UBO is the possible early stage of Myxobolus koi, SBP is the early stage of Sphaerospora branchialis in China. In impression smears we detected developmental stages of SBP in gill and swimbladder. It multiplied by internal budding so that up to 26 secondary cells were formed in each secondary cell, so called "triple formation". We postulated that SBP first revealed in gill, then moved into swimbladder by blood system, at late, transfered into gill again. In the gill the triple formation turned into sporont, the sporont developed into pansporoblast, which includes 12 secondary cells, four of them forming shell valves, four forming polar capsules, fourforming sporoplasms, produced two spore of Sphaerospoa branchialis. When UBOs multiplied largely in blood, some were phagocytized and damaged by macrophages, the amount of leucocytes obviously increased.