This study reports the detection and molecular characterization of Ichthyophthirius multifiliis or freshwater Ich, a parasitic ciliate infecting tank-reared mudfish Channa striata fry. The fry, at 18 days after hatching (DAH), exhibited signs of lethargy, increased mucus secretion, gasping , and eventual death. Prominent white spots, suggestive of I. multifiliis trophonts, were noted on the fry’s body, primarily concentrated on the gills, dorsal, pelvic, and caudal fins.
Samples of the infected fry were collected and the trophonts were individually documented and isolated. Genomic DNA was extracted immediately from the isolated parasite, followed by polymerase chain reaction (PCR) amplification and sequencing of the small-subunit rRNA (SSU rRNA) and mitochondrial cytochrome c oxidase subunit I (MT-COI) regions. BLAST analyses o f the sequences revealed a 100% similarity to the published sequences of I. multifiliis with accession numbers MN372056.1 (Philippines) , OM302502.1 (China), KJ690572.1 (USA), and OM865867.1 (India). The phylogenetic analysis based on SSU rRNA revealed significant bootstrap probability with I. multifiliis , forming distinct clusters independently from other organisms within the order Hymenostomatida. Furthermore, the MT-COI primer failed to amplify the target gene in I. multifiliis . Between both primers it can be said that SSU rRNA gene can be used to detect the parasite in a random target environmental biodiversity screening. This study represents the first documentation and molecular detection of I. multifiliis infection in mudfish C. striata fry.
The protocols presented herein play a crucial role in developing a more rapid and sensitive method for detecting I. multifiliis infections in freshwater fishes in the Philippines.