In order to investigate the ecological regulatory factors influencing Trichodina infection in yellow catfish larvae and juveniles， a population dynamics study of trichodinids was conducted at a yellow catfish seedling farm in Wuhan City， Hubei Province， from May to June 2023.We detected trichodinid infection in yellow catfish larvae and juveniles， identified trichodinid species using morphological and molecular methods， measured physicochemical water quality factors， and quantitatively analyzed plankton.Besides， the correlations between trichodinid infection and aquatic environmental factors were examined using Spearman correlation and redundancy analysis.The results indicated that the prevalence of trichodinid infection ranged from 26.7% to 93.0%， with infection intensity ranging from 1 to 21.Six trichodinid species were identified， including Trichodina hyperparasitis Chen & Hsieh， 1984.The water temperature in the yellow catfish seedling pond ranged from 23.0 ℃ to 31.5 ℃， Secchi disk depth ranged from 53.0 to 109.0 cm， pH ranged from 6.8 to 8.5， ammonia nitrogen concentration ranged from 0.1 to 1.3 mg/L， nitrite nitrogen concentration ranged from 0.003 to 0.020 mg/L.A total of 54 genera and 73 species of zooplankton were identified， with Conochilus unicornis as the dominant species.Zooplankton density ranged from 1 171.30 to 28 712.02 ind./L， biomass ranged from 0.54 to 14.97 mg/L， the Shannon-Wiener diversity index ranged from 0.56 to 1.32， the Pielou evenness index ranged from 0.22 to 0.49 and the Margalef richness index ranged from 2.31 to 4.28.A total of 59 genera and 131 species of phytoplankton have been identified， with Chlorella sp. as the dominant species.Phytoplankton density ranged from 1.88×10⁵ to 5.61×10⁶ ind./L， biomass ranged from 0.38 to 8.04 mg/L， the Shannon-Wiener diversity index ranged from 0.53 to 1.64， the Pielou evenness index ranged from 0.16 to 0.49 and the Margalef richness index ranged from 3.66 to 6.86.Besides， dissolved oxygen， ammonia nitrogen， nitrite nitrogen， feed quantity， rotifer biomass， protozoan biomass， Euglenophyta biomass， Cryptophyta biomass， Pyrrophyta biomass， zooplankton Shannon-Wiener diversity index， and phytoplankton Margalef richness index were the primary aquatic environmental factors.Among these， the ammonia nitrogen and rotifer biomass were the most pivotal factors.Therefore， in practical aquaculture production， the population density of trichodinids can be regulated by adjusting the aforementioned aquatic environmental factors.