Genomic Resources for Sea Lice: Analysis of ESTs and Mitochondrial Genomes

Sea lice are common parasites of both farmed and wild salmon. Salmon farming constitutes an important economic market in North America, South America, and Northern Europe. Infections with sea lice can result in significant production losses. A compilation of genomic information on different genera of sea lice is an important resource for understanding their biology as well as for the study of population genetics and control strategies. We report on over 150,000 expressed sequence tags (ESTs) from five different species (Pacific Lepeophtheirus salmonis (49,672 new ESTs in addition to 14,994 previously reported ESTs), Atlantic L. salmonis (57,349 ESTs), Caligus clemensi (14,821 ESTs), Caligus rogercresseyi (32,135 ESTs), and Lernaeocera branchialis (16,441 ESTs)). For each species, ESTs were assembled into complete or partial genes and annotated by comparisons to known proteins in public databases. In addition, whole mitochondrial (mt) genome sequences of C. clemensi (13,440 bp) and C. rogercresseyi (13,468 bp) were determined and compared to L. salmonis. Both nuclear and mtDNA genes show very high levels of sequence divergence between these ectoparastic copepods suggesting that the different species of sea lice have been in existence for 37–113 million years and that parasitic association with salmonids is also quite ancient. Our ESTs and mtDNA data provide a novel resource for the study of sea louse biology, population genetics, and control strategies. This genomic information provides the material basis for the development of a 38K sea louse microarray that can be used in conjunction with our existing 44K salmon microarray to study host–parasite interactions at the molecular level. This report represents the largest genomic resource for any copepod species to date

Salmon lice ( Lepeophtheirus salmonis

-Temperatures regulate metabolism of marine ectotherms and thereby influence development, reproduction, and, as a consequence, dispersal. Despite the importance of water temperatures in the epidemiology of marine diseases, for the parasitic copepod Lepeophtheirus salmonis, the effect of high and low temperatures has not been methodically investigated. Here, we examined the effects of a wide temperature range (3–20 °C) on L. salmonis larval development, adult body size, reproductive outputs, and infestation success. Further, we tested if dispersal of salmon lice differed with two temperature-dependent development times to the infective stage (30 and 60 degree-days) using an individual-based dispersal model. Development times followed universal models of temperature dependence described for other marine ectotherms. Water temperatures had a negative relationship with development times, adult body size, and reproductive outputs, except at 3 °C, where larvae failed to reach the infective stage and all parameters were decreased, indicating low temperatures are more detrimental than high temperatures. The predictable effect of temperatures on lice development and reproduction will have important applications, such as predicting dispersal and population connectivity, to assist in controlling lice epidemics

Time-series models of sea lice Caligus elongatus (Nordmann) abundance on Atlantic salmon Salmo Salar L. in Loch Sunart, Scotland

Most lice infestations on salmon farmed in the North Atlantic are attributed to Caligus elongatus and Lepeophtheirus salmonis. This study reports findings from time-series analysis conducted on observations of the lesser-studied C. elongatus, in four farms on the west coast of Scotland over the period 1996-2000. Least-squares and Poisson regression techniques were applied to one individual site and to the aggregated data of four sites. Models were fitted and tested for goodness of fit using appropriate statistical methods. Findings indicate that infestation levels are highly seasonal with rapidly increasing numbers after week 22 of the year followed by a steady decline from week 40. Abundance is much lower in the second year of the production cycle than the first. Neither of the models indicated that treatment application has a significant effect on C. elongatus infestations

A mathematical model of the growth of sea lice, Lepeophtheirus salmonis, populations on farmed Atlantic salmon, Salmo salar L., in Scotland and its use in the assessment of treatment strategies

Sea lice are a persistent problem for farmed and wild salmonid populations. Control can be achieved through the use of veterinary medicines. A model was developed to describe the patterns of sea lice infection on salmon farms in Scotland and to predict the likely effect of various treatment strategies. This model takes into account development rates and mortality using compartments representing life history stages and external infection pressure. The national sea lice infection pattern was described using parameters representing stage survival, background infection levels and egg viability rates. The patterns observed across farms varied greatly and the model gave broad agreement to observed trends with different parameters being required in the model for sites using hydrogen peroxide and cypermethrin treatments. The parameter estimates suggest that the background infection pressure on sites where cypermethrin was administered was higher than for those using hydrogen peroxide. Both models had comparable magnitudes of sensitivity with survival from one stage to another being the most sensitive parameter, followed by feedback rates at which gravid females produce eggs, with background infection levels the least sensitive. The effect of different cypermethrin treatment strategies was assessed using the model. Increasing treatments in a production cycle gave more effective control. However, the model showed that timing of treatments is most important if sea lice are to be effectively controlled