Diversity of fungus-like stramenopilous organisms (Oomycota) in Lithuanian freshwater aquaculture: Morphological and molecular analysis, risk to fish health.

The present work is the first comprehensive study of fungus-like stramenopilous organisms (Oomycota) diversity in Lithuanian fish farms aimed at proper identification of saprolegniasis pathogens, which is important for water quality control, monitoring infection levels and choosing more effective treatments for this disease in aquaculture. Pathogenic to fish, Saprolegnia and other potentially pathogenic water moulds were isolated from adult fish, their eggs, fry and from water samples. All detected isolates were examined morphologically and confirmed by sequence-based molecular methods. A total of eight species belonging to the genera Saprolegnia, Achlya, Newbya and Pythium were identified. Four species (S. parasitica, S. ferax, S. australis and S. diclina) were found to be the main causative agents of saprolegniasis in Lithuania. S. parasitica and S. ferax dominated both in hatcheries and open fishponds, accounting for 66.2% of all isolates. S. parasitica was isolated from all farmed salmonid fish species as well as from the skin of Cyprinus carpio, Carassius carassius and Perca fluviatilis. S. australis was isolated from water and once from the skin of Oncorhynchus mykiss, and S. diclina was detected only once on the skin of Salmo salar fish. In addition, Achlya ambisexualis, Saprolegnia anisospora and Newbia oligocantha isolated during this study are noted as a possible source of saprolegniasis. The results of this study are relevant for assessing the risk of potential outbreaks of saprolegniasis or other saprolegnia-like infection in Lithuanian freshwater aquaculture.

Response of ectomycorrhizal and other Pinus sylvestris root-associated fungi to the load of allochthonous material from a great cormorant colony.

Colonies of piscivorous birds nesting in forests bring in loads of allochthonous material in amounts significantly exceeding atmospheric depositions, eventually causing major ecosystem changes. We studied the effect of increasing ornithogenic impact on ectomycorrhizal (EMF) and other root-associated fungi in a Scots pine forest affected by a colony of great cormorants. We evaluated quantitative data of ectomycorrhiza (numbers of root tips and morphotypes) and identified fungal species from pine root tips and from sporocarps collected in three designated study zones: D (zone of active nesting), E (colony margin), and G (pristine forest). Species-bearing sporocarps were absent in zone D, and their number steadily decreased in zone E and was significantly lower than in zone G. Species communities and occurrence frequencies of individual species differed significantly between the zones. Environmental factors, both directly (nutrient addition) and indirectly (changes in vegetation cover), associated with bird activity have significantly influenced fungal communities. We hypothesize that the first signs of increased avian impact on root-associated fungi are the reduced diversity of sporocarps and the low presence and diversity of boletoid fungi in root tips.

Crown fire and surface fire: effects on myxomycetes inhabiting pine plantations.

Myxomycetes are heterotrophic eukaryote organisms that have three life stages, none of which are known to be resistant to fire. The response of myxobiota to different severity of fire is not well known either. We examined myxomycetes in Pinus mugo plantations following a crown fire and in Pinus sylvestris plantations following a surface fire during the first three years after the wildfire event in forested coastal sand dunes in western Lithuania. Additionally, we investigated myxomycetes in corresponding unburned stands. All studied sites (unburned and burned) bore rather different myxomycete assemblages but the disparities of the species compositions between both burn types were more pronounced showing that fire severity had stronger impact on myxomycete species composition than the pre-fire stand type. Analysis of myxomycete assemblages (including the results from field collections, bark and litter cultures) showed that surface fire sites bore the highest number of post-fire species compared to crown fire and unburned sites. Dynamic annual changes in species composition were observed in all studied sites but only crown fire plots showed a clear chronosequence of post-fire myxomycete assemblages. Fire impact promoted establishment and/or sporulation of myxomycete species that are rare in similar unburned stands, or are usually confined to other types of forests and substrata. In addition, individual myxomycete species tended to switch substratum usage during the course of vegetation succession, with a final return to their usual substrata. This possibly signaled the end of early stage of post-fire succession.