Comparison of Host Selection and Gene Expression of Adult Lepeophtheirus Salmonis and Salmo Salar During a Cohabitation of Initially Infected and Uninfected Fish

Heather J Wotton

doi:10.4172/2155-9546.1000226

Abstract

Lepeophtheirus salmonis is a common parasite of salmonid fish and has a significant economic impact on Atlantic salmon (Salmo salar) fish farms. Over time L. salmonis has developed resistance to a number of chemotherapeutants, making the discovery of new treatments important to maintain a profitable farming industry. Determining processes in both L. salmonis and Atlantic salmon important to host selection and colonization may provide new targets for treatment development. During a two week cohabitation of L. salmonis infected and uninfected Atlantic salmon, we were able to collect information on the ability of L. salmonis to switch hosts, and preference for infected or uninfected fish. Whole L. salmonis and Atlantic salmon tissues were collected at 2 and 14 days post cohabitation to determine if differential gene expression was occurring during this process. At 2 days post cohabitation there was no significant difference in the number of male lice on the initially infected and uninfected fish. Eight L. salmonis genes putatively associated with various facets of lice survival (CYP18 A1-like, cytochrome p450 Isoform 1-like protein, glycene receptor α-2-like, leukocyte receptor cluster member 9-like, nicotinic acetylcholine receptor subunit-like, tissue plasminogen activator precursor-like, peroxinectin-like, and Trypsin-1) were analysed in both adult male and female lice, as well as five genes indicating immune status in Atlantic salmon. Comparisons were made to look for differential gene regulation as well as correlation between expression of L. salmonis genes and Atlantic salmon genes. Only MMP9 expression in salmon spleen was differentially regulated during the study period, however, correlations between the expression of several louse and salmon genes were found. Notably, the expression of a peroxinectin-like gene in male and female L. salmonis was correlated with the expression of IL-1, IL-12, IgT and matrix metalloproteinase 9 intermittently in salmon. This paper provides new insight into the interactions between L. salmonis and S. salar during infection.

Highlights

Lepeophtheirus salmonis is a species of parasitic crustacean commonly referred to as sea lice
Infected Atlantic salmon had been infected with laboratory reared L. salmonis copepodids 72 days prior to the beginning of cohabitation, and individual lice numbers on each infected fish was recorded as it was transferred into the study tanks
The lack of movement of adult female L. salmonis observed in this study compared to the movement of preadult II L. salmonis and adult C. elongatus in the two previous experiments may be attributed to morphological and energical demands associated with reproduction

Summary

Introduction

Lepeophtheirus salmonis is a species of parasitic crustacean commonly referred to as sea lice. This species of lice has a circumpolar distribution, infecting fish in the marine waters of the Northern Hemisphere. Lepeophtheirus salmonis is primarily a parasite of salmonids, and is pathogenic to Atlantic salmon (Salmo salar). Management of L. salmonis infection on farmed Atlantic salmon is imperative to the aquaculture industry, as sea lice can cause significant damage to salmon as they feed. Total impact of sea lice infestation of Atlantic salmon on the aquaculture industry has a cost of nearly $500USD million annually, due to reduced value of final product and use of parasiticides [7]

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