Impact of abiotic factors and husbandry on saprolegniosis in salmonid farms

Abstract

Oomycetes of the genus Saprolegnia are widespread in freshwater environment and are among the main path-
\nogens causing economic losses in salmonid aquaculture.
\nInfections by mycotic agents in fish farming are generally considered to result from chronic stress and poor fish
\ncondition associated with water quality problems, adverse environmental conditions, frequent/rough/incorrect
\nhandling, concurrent infections, physiological changes associated with reproduction and immunocompromised
\nanimals.
\nTo identify risk factors for Saprolegnia infections in trout and Atlantic salmon farming, longitudinal studies
\nwere carried out in different Italian, Spanish, and Scottish fish farms. Prevalence of saprolegniosis and fish
\nmortality were monitored over time and statistically analysed with respect to husbandry and environmental
\nfactors.
\nOverall, statistical results by production cycle (trout vs salmon farming) and by country indicate that the
\nprevalence of Saprolegnia may be influenced by peculiarities of the culture system and farming environment.
\nNevertheless, a specific set of parameters, including lower water temperature, and handling procedures increased
\nSaprolegnia prevalence in all the considered farms. Particularly, in trout farms Saprolegnia infections represented
\nan important contribution to mortality, and prevalence was influenced by water temperature and pH, and by fish
\ndensity within the tanks. Similarly, temperature and water quality were the main factors influencing the prev-
\nalence of Saprolegnia in Atlantic salmon farms. Moreover, molecular analyses confirmed the role of S. parasitica as
\nthe main pathogenic oomycete in trout and salmon farming in the considered countries. The identification of risk
\nfactors for introduction and increase of Saprolegnia infection in fish farms will allow the correct design of bio-
\nsecurity and pathogen control strategies

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