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

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

doi:10.3390/pathogens10080926

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.

Highlights

IntroductionOne of the main issues related to intensive aquaculture is the proliferation of parasites, those with direct life cycles, and other infectious agents due to high farming densities [2], which can subsequently spread outside the farm into the natural environment
Parasites of wild fish pose a potential threat to aquaculture [1]
Environmental Parameters In Italian trout farms, recorded values of Dissolved Oxygen (DO) ranged from 3.9 to 16.8, with a median of 9.7 ppm (IQRs: 7.7–10.6), water temperatures ranged from a minimum of 5.1 to a maximum of 14.2 ◦ C with a median of 11.6 ◦ C (IQRs: 9.5–12.5)

Summary

Introduction

One of the main issues related to intensive aquaculture is the proliferation of parasites, those with direct life cycles, and other infectious agents due to high farming densities [2], which can subsequently spread outside the farm into the natural environment. The risk of diseases spreading from wild to farmed fish, with subsequent proliferation within the farm and transmission into the environment, generates great concern. Severe problems with respect to parasite exchange between farmed and wild fish have been reported [3,4,5]. Salmonid farming is mainly based on open aquaculture systems (open-net pens, raceways), which exchange water together with other materials, such as chemicals, waste, and a wide range of potential infectious agents with the natural environment (sea, natural streams). The introduction of potentially pathogenic oomycete species into lakes and ponds through fish stocking and other anthropogenic activities has been associated with the decline of amphibian [7] and crustacean [8,9] populations

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