Distribution and environmental preferences of Saprolegnia and Leptolegnia (Oomycota) species in fish hatcheries in Hungary

Here, we studied for the first time the abundance and species distribution of water moulds (Oomycota, Saprolegniales) in fish hatcheries in Hungary, focusing on Saprolegnia and Leptolegnia spp. A total of 182 water mould isolates were obtained from different developmental stages of fish (eggs, fry and adults), and from water samples during the spawning season of cyprinids and salmonids. Of the ten water mould species identified by ITS–rDNA sequences, S. parasitica, S. ferax and S. australis were the most abundant ones. The statistical analyses of species proportions in relation to sample source and host preference revealed that S. parasitica was significantly more abundant in the host than in the water sample, whereas the opposite trend was observed for S. ferax and S. australis. In addition, our results confirmed previous findings that S. australis and S. ferax prefer warm water (+21–24°C) and that S. parasitica has a wide temperature tolerance (+3–24°C). The DNA sequence identity analysis showed that the species demarcation criterion for Saprolegnia spp. is approximately 98% identity based on ITS–rDNA sequences. Furthermore, our phylogenetic analyses suggest that a taxonomic revision of Leptolegnia spp. is necessary.