Susceptibility of rainbow trout Oncorhynchus mykiss, Atlantic salmon Salmo salar and coho salmon Oncorhynchus kisutch to experimental infection with sea lice Lepeophtheirus salmonis.
Physiological, immunological and biochemical parameters of blood and mucus, as well as skin histology, were compared in 3 salmonid species (rainbow trout Oncorhynchus mykiss, Atlantic salmon Salmo salar and coho salmon O. kisutch) following experimental infection with sea lice Lepeophtheirus salmonis. The 3 salmonid species were cohabited in order to standardize initial infection conditions. Lice density was significantly reduced on coho salmon within 7 to 14 d, while lice persisted in higher numbers on rainbow trout and Atlantic salmon. Lice matured more slowly on coho salmon than on the other 2 species, and maturation was slightly slower on rainbow trout than on Atlantic salmon. Head kidney macrophages from infected Atlantic salmon had diminished respiratory burst and phagocytic capacity at 14 and 21 d post-infection (dpi), while infected rainbow trout macrophages had reduced respiratory burst and phagocytic capacities at 21 dpi, compared to controls. The slower development of lice, coupled with delayed suppression of immune parameters, suggests that rainbow trout are slightly more resistant to lice than Atlantic salmon. Infected rainbow trout and Atlantic salmon showed increases in mucus lysozyme activities at 1 dpi, which decreased over the rest of the study. Mucus lysozyme activities of infected rainbow trout, however, remained higher than controls over the entire period. Coho salmon lysozyme activities did not increase in infected fish until 21 dpi. Mucus alkaline phosphatase levels were also higher in infected Atlantic salmon compared to controls at 3 and 21 dpi. Low molecular weight (LMW) proteases increased in infected rainbow trout and Atlantic salmon between 14 and 21 dpi. Histological analysis of the outer epithelium revealed mucus cell hypertrophy in rainbow trout and Atlantic salmon following infection. Plasma cortisol, glucose, electrolyte and protein concentrations and hematocrit all remained within physiological limits for each species, with no differences occurring between infected and control fish. Our results demonstrate that significant differences in mucus biochemistry and numbers of L. salmonis occur between these species.
Fast
Mark D
MD
Department of Anatomy and Physiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island C1A 4P3, Canada.
Ross
Neil W
NW
Mustafa
Ahmed
A
Sims
David E
DE
Johnson
Stewart C
SC
Conboy
Gary A
GA
Speare
David J
DJ
Johnson
Gerald
G
Burka
John F
JF
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D033342:Copepoda / Q000254:growth & development* / Q000472:pathogenicity; D004198:Disease Susceptibility / Q000662:veterinary; D004478:Ectoparasitic Infestations / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*; D005393:Fish Diseases / Q000276:immunology* / Q000469:parasitology; D006790:Host-Parasite Interactions; D009093:Mucus / Q000166:cytology / Q000201:enzymology / Q000276:immunology; D009113:Muramidase / Q000378:metabolism; D017684:Oncorhynchus kisutch; D017686:Oncorhynchus mykiss; D010587:Phagocytosis; D020317:Salmo salar; D012867:Skin / Q000166:cytology / Q000201:enzymology / Q000276:immunology; D013045:Species Specificity
D000469:Alkaline Phosphatase; D009113:Muramidase