Comprehensive assessment of Saprolegniaceae in two Brazilian trout farms

Members of the family Saprolegniaceae are widely recognized as pathogens in salmonid aquaculture worldwide. In the present study, we investigated the presence and diversity of Saprolegniaceae in two trout farms located in Campos do Jordão, São Paulo State, Brazil. Sampling included the water supply, rearing tanks across various developmental stages of trout, as well as trout eggs and deceased fish. A total of 167 isolates were obtained using a baiting technique. These isolates were identified through both morphological and molecular analyses and were assigned to the genera Cokeria , Newbya , and Saprolegnia . Cokeria radiosa was the most frequently isolated species across the two farms. Notably, Newbya oblongata was sequenced for the first time and is here reported for the first time in Brazil. All species identified in this study have previously been reported in association with trout and trout eggs in other regions of the world. This study represents the first comprehensive assessment of Saprolegniaceae diversity in Brazilian trout farming systems. The findings contribute to a better understanding of the distribution and ecology of these zoosporic organisms in aquaculture environments and support future efforts in monitoring and managing potential pathogenic species in fish farming operations.