Publication
The effects of environmental factors on mortality and complex gill disease in Scottish farmed Atlantic salmon (Salmo salar L.) using a time series analysis
| Summary: | Environmental factors influence the productivity of the salmon aquaculture industry in Scotland. Variation of environmental parameters has been associated with increasing mortalities and economic losses to the producers. Additionally, Complex Gill Disease (CGD) is emerging as a significant challenge for the salmon industry, and it is believed that its influence is dependent on the environmental conditions at farms before outbreaks. Using salmon mortality data reported monthly as an outcome and satellite environmental data (temperature, salinity, and phytoplankton) as the explanatory variables, the first part of this study included a linear mixed model with a time series analysis to investigate the association between these variables. The modelling results showed a positive significant association between temperature and salmon mortality. The second part of the study included data from eight salmon farms and comprised of histopathological and gross gill scoring, RT-PCR analysis for the four most commonly associated pathogens to CGD (Neoparamoeba perurans, Candidatus Branchiomonas cysticola, Salmon Gill Poxvirus (SGPV) and Desmozoon lepeophtherii), amongst others. Histopathological gill scores were used to develop a case definition for CGD and use the presence of disease in the fish as outcome. The prevalence of CGD was 10% in the study population. Farm data and satellite environmental data (temperature, salinity, phytoplankton, chlorophyll, dissolved oxygen (DO), and rainfall) were used as explanatory variables to a generalized linear mixed model with a time series analysis to investigate their association with the development of CGD. Significant interactions between RT-PCR results of Ca. B. cysticola and DO and between results of N. perurans and rainfall were described in this study. These interactions, together with gross gill scores and chlorophyll were significantly associated with the appearance of CGD cases in the salmon. Results on the study conducted demonstrated that, in fact, environmental factors have an impact on salmon mortalities and gill health. Environmental factors should, therefore, be monitored and control measures should be employed to reduce losses and the development of disease related to environmental conditions in salmon farms. |
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| Main Authors: | Ferreira, Ana Rita Isidoro |
| Subject: | Atlantic salmon Environmental factors Mortality Complex Gill disease Mixed models Salmão do Atlântico Fatores ambientais Mortalidade Doença complexa das guelras Modelos mistos |
| Year: | 2021 |
| Country: | Portugal |
| Document type: | master thesis |
| Access type: | open access |
| Associated institution: | Universidade de Lisboa |
| Language: | English |
| Origin: | Repositório da Universidade de Lisboa |
| Summary: | Environmental factors influence the productivity of the salmon aquaculture industry in Scotland. Variation of environmental parameters has been associated with increasing mortalities and economic losses to the producers. Additionally, Complex Gill Disease (CGD) is emerging as a significant challenge for the salmon industry, and it is believed that its influence is dependent on the environmental conditions at farms before outbreaks. Using salmon mortality data reported monthly as an outcome and satellite environmental data (temperature, salinity, and phytoplankton) as the explanatory variables, the first part of this study included a linear mixed model with a time series analysis to investigate the association between these variables. The modelling results showed a positive significant association between temperature and salmon mortality. The second part of the study included data from eight salmon farms and comprised of histopathological and gross gill scoring, RT-PCR analysis for the four most commonly associated pathogens to CGD (Neoparamoeba perurans, Candidatus Branchiomonas cysticola, Salmon Gill Poxvirus (SGPV) and Desmozoon lepeophtherii), amongst others. Histopathological gill scores were used to develop a case definition for CGD and use the presence of disease in the fish as outcome. The prevalence of CGD was 10% in the study population. Farm data and satellite environmental data (temperature, salinity, phytoplankton, chlorophyll, dissolved oxygen (DO), and rainfall) were used as explanatory variables to a generalized linear mixed model with a time series analysis to investigate their association with the development of CGD. Significant interactions between RT-PCR results of Ca. B. cysticola and DO and between results of N. perurans and rainfall were described in this study. These interactions, together with gross gill scores and chlorophyll were significantly associated with the appearance of CGD cases in the salmon. Results on the study conducted demonstrated that, in fact, environmental factors have an impact on salmon mortalities and gill health. Environmental factors should, therefore, be monitored and control measures should be employed to reduce losses and the development of disease related to environmental conditions in salmon farms. |
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