STUDIES INTO THE POSSIBLE PROTOZOAN ETIOLOGY OF SWIMBLADDER INFLAMMATION IN CARP FRY

Laboratory examinations of pond-reared common carp, C. carpio l., revealed a close correlation between the prevalence of swimbladder inflammation (SBI), renal sphaerosporosis and infection by C-blood-protozoan among the carp fry. In impression smears as well as light microscopic and EM preparations developmental stages of intercellular protozoa were detected mainly in the loose fibrous tissue of swimbladder. The parasites multiplied by internal budding so that 20-46 secondary cells were formed in each primary cell and 2 tertiary cells were formed in each secondary cell. The final stage of development was a unit consisting of a secondary cell enclosing 2 tertiary cells, i.e., a so-called triple formation, which bore a close resemblance to the early sporogonic stages of the renal sphaerosporan Sphaerospora angulata. Certain morphological similarities and the frequent simultaneous presence of the swimbladder protozoan, C-blood-protozoan, and S. angulata in hosts with clinical SBI have led us to postulate that the former 2 parasites could represent the previously unknown presporogonic stages of S. angulata. In view of the pathological changes caused by the parasites in the hosts with clinical SBI, and negative bacteriological and virological findings, we have postulated that the swimbladder protozoan is the primary cause of SBI in carp fry.