Variation in host preference within Gyrodactylus salaris (Monogenea): an experimental approach.

Area of Science:

• Ichthyoparasitology
• Aquatic Ecology
• Fish Health Management

Background:

• Gyrodactylus salaris (G. salaris) is a monogenean ectoparasite devastating wild Atlantic salmon (Salmo salar) populations in Norway.
• A G. salaris population in Lake Pålsbufjorden infects resident Arctic charr (Salvelinus alpinus) without affecting downstream Atlantic salmon.

Purpose of the Study:

• To experimentally assess the infectivity and reproductive capacity of G. salaris from Arctic charr to Atlantic salmon, Arctic charr, and rainbow trout (Oncorhynchus mykiss).
• To determine if the G. salaris population from Lake Pålsbufjorden poses a threat to Atlantic salmon populations.

Main Methods:

• Experimental infection trials using G. salaris isolated from Arctic charr.
• Testing infectivity and reproductive success on Atlantic salmon (wild and hatchery-reared), Arctic charr, and rainbow trout.
• Comparative analysis of G. salaris virulence across different fish hosts.

Main Results:

• Arctic charr and rainbow trout exhibited moderate susceptibility to G. salaris.
• Atlantic salmon stocks from River Numedalslågen and River Drammenselva showed innate resistance to slight susceptibility.
• G. salaris from Arctic charr in Lake Pålsbufjorden was non-pathogenic to Atlantic salmon.

Conclusions:

• The G. salaris population in Lake Pålsbufjorden demonstrates a specific host preference and is non-pathogenic to Atlantic salmon.
• This finding represents the first documented variation in host preference among Norwegian G. salaris populations.
• Observed differences in parasite virulence have significant implications for international legislation and management strategies for Atlantic salmon.