First Investigation of Trichodinid Species (Ciliophora: Trichodinidae) on Farmed Hybrid Yellow Catfish (Tachysurus fulvidraco × Tachysurus vachelli) in China.

Hybrid yellow catfish (Tachysurus fulvidraco♀ × Tachysurus vachelli♂) is a significant aquaculture variety in China. It is easy to be infected by trichodinids, causing serious economic losses. However, the species investigation of trichodinids on hybrid yellow catfish is relatively deficient, which seriously hinders the prevention and control of trichodiniasis. Hence, trichodinids were collected in a hybrid yellow catfish farm in Hubei Province from June 2022 to October 2023 and identified by morphological and molecular biology methods. A new species Tripartiella luhuensis sp. nov. and nine Trichodina species were described. Phylogenetic analyses demonstrated that T. luhuensis nested in the Trichodinella-Tripartiella-Paratrichodina clade, indicating that the genus Tripartiella is not a monophyletic group. Besides, Trichodinid species from Siluriformes hosts have relatively similar evolutionary positions. Histopathological analysis revealed that the parasitism of trichodinids caused mechanical damage and mucus hypersecretion to gill of the host. The present study reports trichodinid species on hybrid yellow catfish for the first time and adds one new species to the genus Tripartiella. We also indicate the importance of preventing and controlling trichodiniasis in hybrid yellow catfish farming.