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. 2021 Jul 22;10(8):926.
doi: 10.3390/pathogens10080926.

Evaluation of Potential Transfer of the Pathogen Saprolegnia parasitica between Farmed Salmonids and Wild Fish

Perla Tedesco  1 , Marcia Saraiva  2 , Jose Vladimir Sandoval-Sierra  3   4 , Maria Letizia Fioravanti  1 , Benedetto Morandi  1 , Javier Dieguez-Uribeondo  3 , Pieter van West  2 , Roberta Galuppi  1
Affiliations

Evaluation of Potential Transfer of the Pathogen Saprolegnia parasitica between Farmed Salmonids and Wild Fish

Perla Tedesco et al. Pathogens. .

Abstract

Saprolegnia infections are among the main parasitic diseases affecting farmed salmonids. The distribution and potential transfer of Saprolegnia spp. between farms and the natural environment has been scarcely investigated. Therefore, this work aimed to study the diversity and abundance of oomycete species in salmonid farms, tributary water, and effluent water systems. Four trout farms in Italy and two Atlantic salmon farms in Scotland were considered. In Italian farms, 532 isolates of oomycetes were obtained from fish and water, at upstream, inside, and downstream the farms. In Scottish farms, 201 oomycetes isolates were obtained from water outside the farm and from fish and water inside the farming units. Isolates were identified to the species level through amplification and sequencing of the ITS rDNA region. In Italy, S. parasitica was significantly more present in farmed than in wild fish, while in water it was more frequently isolated from the wild, particularly in effluent systems, not associated with more frequent isolation of S. parasitica in wild fish downstream the farm. In Scotland, S. parasitica was the most prevalent species isolated from fish, while isolates from water were mostly Pythium spp. with few S. parasitica isolates from upstream and downstream the farms.

Keywords: Italy; Oncorhynchus mykiss; Salmo marmoratus; Salmo salar; Salmo trutta; Saprolegnia parasitica; Scotland; salmonid farms.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
(a) distribution of Dissolved Oxygen, temperature, and pH values collected during the visits in Italian farms; (b) Correlation between Oxygen saturation and water temperature in Italian farms (rho = 0.6152, p < 0.0001).
Figure 2
Figure 2
Pearson’s correlation coefficients calculated considering environmental data from Scottish farms.
Figure 3
Figure 3
Maximum Likelihood tree based on ITS nrDNA sequences of oomycetes isolated during the present study with indication of the MOTUs (in bold) identified.
Figure 4
Figure 4
Frequencies of S. parasitica detected within the four Italian farms and the relative 95% CIs. Pairwise comparisons showed differences between farm A and B; B and C and B and D (Fischer’s exact p < 0.001), and between farm C and D (p = 0.002). Different letters indicate significant difference.
Figure 5
Figure 5
Species composition of oomycetes isolated from fish and water in Italian (a) and Scottish (b) farms.
Figure 6
Figure 6
Isolation of S. parasitica in fish and water from upstream (before), in-farm (inside) or downstream (after) sampling sites in Italy.
Figure 7
Figure 7
Farms considered for the study. (A) Farms’ location in Italy, (B) Farms’ location in Scotland.
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