Susceptibility of rainbow trout Oncorhynchus mykiss, Atlantic salmon Salmo salar and coho salmon Oncorhynchus kisutch to experimental infection with sea lice Lepeophtheirus salmonis

Abstract

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. KEY WORDS: Skin mucus · Lysozyme · Sea lice · Protease · Alkaline phosphatase · Salmonids · ImmunityResale or republication not permitted without written consent of the publisher

Development of the salmon louse Lepeophtheirus salmonis and its effects on juvenile sockeye salmon Oncorhynchus nerka

“…Furthermore, mortality and the highest mean plasma osmolality and plasma cortisol values occurred in Trial 3, suggesting that in juvenile sockeye salmon, very high parasite intensities induced an added physiological burden that was independent of host size and probably directly related to a loss of skin integrity (Bjørn & Finstad 1998, Bowers et al 2000, Finstad et al 2000. The coincidence of significant plasma cortisol responses with the first detection of mobile Lepeophtheirus salmonis in sockeye salmon is similar to the timing of responses measured in Atlantic and chum salmon during laboratory L. salmonis infections (Bowers et al 2000, Fast et al 2002, Jones et al 2007. Plasma cortisol levels also increased in sea trout during infections with chalimus stages of L. salmonis (Bjørn & Finstad 1997).…”

“…In the present study, louse survival at 7, 8 and 10 dpi was 16, 18 and 20%, respectively, in the 3 trials, suggesting that susceptibility of juvenile sockeye salmon to L. salmonis is intermediate between that of pink and Atlantic salmon. Comparative data from previous studies indicate that rejection of L. salmonis is host species dependent: lice are rejected more rapidly from pink and coho salmon than from chum, Chinook or Atlantic salmon or from rainbow trout, and lice tend to be rejected from pink and coho salmon during chalimus stages of development (Johnson & Albright 1992, Fast et al 2002, Jones et al 2007. Whereas the retention of higher numbers of more aggressive mobile parasites contributes to the pathology observed on susceptible salmon, concurrent development of epithelial pathology in coho salmon or of the expression of proinflammatory genes in skin of pink salmon (Johnson & Albright 1992, Jones et al 2007, Braden et al 2012 suggests that cutaneous inflammation is partly responsible for rejection of lice from less susceptible salmon.…”

“…Johnson & Fast (2004) corrected for some of these factors by comparing different experiments based on the lice infection densities on Atlantic salmon. Despite similarities in study design resulting in 0.16 lice g −1 fish at the time of moult to pre-adult, cortisol levels were 7.3 ng ml −1 in Fast et al (2002) and ranged from 54.5 to 72.7 ng ml −1 in Bowers et al (2000). Plasma cortisol levels in juvenile chum salmon were 80 ng ml −1 in exposed fish and 15 ng ml −1 in controls at 21 dpi, with an infection density of 0.08 lice g −1 fish (Jones et al 2007).…”

“…For example, a well-developed tissue response occurs at the site of louse attachment on coho salmon Oncorhynchus kisutch 1 d post infection, whereas the reaction is markedly reduced or absent in Chinook salmon O. tshawytscha and Atlantic salmon (Johnson & Albright 1992). Similarly, the intensity of L. salmonis was significantly lower on coho salmon when compared to Atlantic salmon and rainbow trout O. mykiss (Fast et al 2002), and pink salmon O. gorbuscha rejected L. salmonis more rapidly than chum salmon O. keta during laboratory challenges (Jones et al 2006(Jones et al , 2007. The rejection of lice observed in the latter study is associated with an earlier and quantitatively higher expression of proinflammatory genes in pink salmon (Jones et al 2007).…”

Molecular profiling of the gilthead sea bream (Sparus aurata L.) response to chronic exposure to the myxosporean parasite Enteromyxum leei

“…In a subsequent study investigating the effects of gilthead sea bream nutritional status on E. leei disease progression, total serum peroxidases, lysozyme and nitric oxide were also significantly reduced in exposed fish fed either fish oil or a vegetable oil-based diet (Estensoro et al, 2011). Other immune parameters such as the phagocytic activity of macrophages and/or respiratory burst of leukocytes were also decreased in different hosts infected with other parasites (Mustafa et al, 2000;Fast et al, 2002;Scharsack et al, 2004;Karagouni et al, 2005). At the transcriptional level, the parasite-mediated amoebic gill disease (AGD) in Atlantic salmon produced a marked up-regulation of gene expression in early stages (4-8 days) of infection (Morrison et al, 2006), whereas at medium (19 days) (Wynne et al, 2008a) and long term exposure (36 days) (Young et al, 2008), a strong overall gene suppression was evident in the immune response, transport, translation and catalytic activity functional categories.…”