Detection and Identification of Paragyliauchen sp. (Trematoda) and Bacteria in Diseased Centropyge bicolor from the European Marine Aquarium Trade

During the examination of a bicolor angelfish (<i>Centropyge bicolor</i>) imported from the Philippines and intended for sale on the Polish market, clinical signs of weakness and respiratory distress were observed. Mild hyperemia was noted along the lateral sides of the body and around the mouth. Necropsy revealed the presence of five orange-colored trematodes in the intestinal lumen, with an average body length of 3.12 mm. Based on morphological features and molecular analyses, the parasite was identified as <i>Paragyiauchen</i> sp. The following gene loci were amplified: the gene-encoding component of the large ribosomal subunit (<i>28S rRNA</i>), the gene-encoding NADH dehydrogenase subunit 1 (<i>ND1</i>), the gene cluster <i>5.8S rRNA-ITS2-28S rRNA</i> and the gene cluster <i>ITS2-28S rRNA</i>. Bacterial species identification using MALDI-TOF MS revealed the presence of three species: <i>Shewanella putrefaciens</i> and <i>Brevundimonas diminuta</i> isolated from the head kidney, and <i>Aeromonas caviae</i> isolated from the liver. This study documents the first detection of representatives of <i>Paragyliauchen</i> genus in <i>C. bicolor</i> imported to Europe and highlights the potential risk of introducing new parasites and opportunistic bacterial pathogens through the ornamental fish trade. These findings emphasize the need for parasitological and microbiological screening of imported ornamental fish.