Genetic variation in parasite resistance of Atlantic salmon to amoebic gill disease over multiple infections

• Published in: Aquaculture Vol. 364-365; pp. 165 - 172
• Main Authors: Kube, Peter D., Taylor, Richard S., Elliott, Nicholas G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 05-10-2012; Elsevier Sequoia S.A
• Subjects: Amoebic gill disease; Animal diseases; animal parasites and pests; Aquaculture; Atlantic salmon; disease control; Disease resistance; fish industry; genetic correlation; Genetic diversity; genetic traits; genetic variation; gills; Heritability; immunity; Immunity (Disease); livestock; Marine; Neoparamoeba; Parasites; parasitoses; Salmo salar; Salmon; Salmonidae; Selective breeding; sires; Disease resistance; Atlantic salmon; Heritability; Selective breeding; Salmo salar; Amoebic gill disease
• ISSN: 0044-8486; 1873-5622
• DOI: 10.1016/j.aquaculture.2012.08.026

Genetic selection is being developed as a management tool for the control of amoebic gill disease (AGD) in Atlantic salmon. AGD is caused by an external gill parasite and is an animal health issue that results in significant economic loss to the Tasmanian salmon industry. This paper presents genetic parameters for AGD resistance, describes patterns of genetic variation over multiple infection cycles, and discusses the development of a selective breeding program to exploit this variation.
Measurements of visible gill signs were made on over 12,000 individuals representing 326 sires and 297 dams from four genetically linked year classes. Between three and six sequential infections were measured on each year class. All measures of gill signs in all year classes had significant genetic variation with heritabilities ranging from 0.09±0.03 to 0.56±0.07. Genetic correlations between infections indicate two distinct traits which are only weakly correlated (average rg=0.24). One is measured at first infection on naïve fish and the other can be measured at all subsequent infections. This pattern is suggestive of an adaptive immune response for reinfections, and conforms with patterns seen for resistance to other parasitic diseases in terrestrial livestock. In an analysis combining all year classes, the heritability for first infection was 0.14±0.02 and heritabilities for reinfections ranged from 0.23±0.08 to 0.40±0.03. Reinfections appeared to be mostly under common genetic control, although there appear to be additional genetic traits that cause lower correlations for a small proportion (about 10%) of the population. Consistent and stable patterns of inheritance are indicated by the medium to high genetic correlations between year classes and by the high genetic correlations between infection cycles with a seasonal shift. Estimation of genetic correlations between AGD resistance and growth rate are problematic due to confounding effects but it is likely that this correlation is near zero.
Selection for AGD resistance can assist with disease management and is part of the breeding objective of the Tasmanian salmon breeding program. Adaptive AGD resistance is one of the primary selection traits and a field challenge based on assessment of gill signs is an effective way of selecting for resistance. The current selective breeding strategy is predicted to increase the interval between treatments by 3% per year.
► Resistance to amoebic gill disease in Atlantic salmon is under genetic control. ► There are two distinct traits, one at first infection and the other at all subsequent infections. ► This pattern is suggestive of an adaptive immune response for reinfections. ► Heritability for first infection was 0.14 and from 0.22 to 0.35 for reinfections. ► Selection for resistance is being used by the Tasmanian Atlantic salmon industry.