Molecular Identification of Spironucleus vortens From the Digestive Tract of Discus (Symphysodon discus Heckel, 1840) and Its Association With Mixed Bacterial Coinfection

ABSTRACT This study presents the first case in Poland of isolation and molecular identification of the Spironucleus vortens parasite from the digestive tract of diseased ornamental fish belonging to the species discus fish ( Symphysodon discus Heckel, 1840). Recently, an increasing percentage of fish submitted for testing to the Department of Biology and Fish Diseases, have been observed that show typical symptoms of hole‐in‐the‐head disease, therefore it is important to have accurate information about this disease. In preparation of this work, two fish were studied. The polymerase chain reaction (PCR) used a pair of primers designed specifically for this experiment. The amplification product was sequenced and the partial sequence of small ribosomal subunit (18S rRNA) was deposited in the GenBank database. The obtained nucleotide sequence showed a high percentage of identity with the compared sequence of the S . vortens reference strain (98.52%). Additionally, the presence of potentially dangerous bacteria belonging to four species, namely Citrobacter braakii , Acinetobacter lwoffi , Pseudomonas putida and Comamonas testosteroni was confirmed in the material collected from the tested fish. Bacterial isolates were examined biochemically. An antibiotic susceptibility testing showed that in three of the four isolates there appeared resistance to the drugs used. Trial Registration: Clinical trial registration was not required for this study.