North Pacific Anadromous Fish Commission

The Role of Parasitic Pathogens in the Population Dynamics of Anadromous Salmonids in the North Pacific and North Atlantic Oceans: A Review

Authors:
Shigehiko Urawa and Shinya Mizuno

Abstract:
Numerous parasite species have been recorded from anadromous salmonids in the North Pacific and North Atlantic oceans, and they occasionally play a significant role in regulating wild fish populations. This paper focuses on three types of parasitic pathogens that affect the migration, growth and survival of salmonids in the marine environment: the ectoparasitic protozoan Ichthyobodo salmonis, the endoparasitic trematode Nanophyetus salmincola, and salmon louse (crustacean) Lepeophtheirus salmonis. The euryhaline flagellate I. salmonis attaches on the skin and gills of chum salmon (Oncorhynchus keta) and Atlantic salmon (Salmo salar). Juvenile chum salmon suffer from severe skin damage due to the heavy parasite infection. This impairs their ability to maintain osmotic balance and leads to significant mortalities when they enter the coastal saline waters. The metacercarial stage of digenean N. salmincola is primarily found in the kidney and muscle of Chinook (O. tshawytscha) and coho salmon (O. kisutch) in coastal rivers of the Pacific Northwest. The parasite has negative effects on the swimming performance, growth, osmoregulation, immune function, and disease resistance of juvenile salmon, and parasite-associated host mortalities occur during the early marine residence. The salmon louse L. salmonis is a common parasitic copepod that feeds on the skin, mucus and blood of various salmonids in the North Pacific and North Atlantic oceans. The salmon louse has high impacts on the migration behavior, growth and survival of wild salmon and sea trout (S. trutta) especially in the coastal waters where high densities of lice larvae are released from farmed salmon. Multiple environmental and intrinsic factors influence the interactions between parasites and host fishes. A comprehensive approach to investigate how parasites affect the population dynamics of wild salmonids requires a combination of field and laboratory experiments as well as modeling studies that consider various environmental and biotic factors.

DOI:
https://doi.org/10.23849/npafcb7/p9-wjakh

Citation

Urawa, S., and S. Mizuno.  2024.  The role of parasitic pathogens in the population dynamics of anadromous salmonids in the North Pacific and North Atlantic oceans: a review.  N. Pac. Anadr. Fish Comm. Bull. 7: 19–35.  https://doi.org/10.23849/npafcb7/p9-wjakh