A novel lice control method: photochemical treatment (Photolice)

Control of salmon lice has long been the biggest challenge for the further development of a sustainable industry. Preventive measures are expected to play an increasing role, but experience suggests that drug treatment will still be an important tool in an effective lice strategy. Today's control options are limited by unwanted environmental effects or resistance issues linked to the use of chemicals. This project has tested whether light-activated chemicals used in e.g. human cancer medicine could be an effective and environmentally friendly treatment method against salmon lice. The project consisted of three parts, which first examined the direct effect of substances on salmon lice (screening phase), after which selected substances were tested on lice-infected fish and finally on organisms from the environment around the cage. Nine different compounds were tested, where three of the tested compounds induced mortality when applied directly to salmon lice but did not induce loss of salmon lice when applied to infected fish. The tested compounds had no negative effects on fish welfare, nor did they induce mortality or change the behavior of rock-pool shrimps, which were used as an example of an organism that might be affected. We conclude that the use of photoactivated compounds may be possible to eliminate salmon lice from fish in aquaculture environments, but further studies are necessary.A novel lice control method: photochemical treatment (Photolice)publishedVersio

Temperaturens innflytelse på lakseluslarver. Sluttrapport FHF-prosjekt 901073

Engelsk: Development and survival time of salmon lice (Lepeophtheirus salmonis) larvae are temperature dependent. The potential for spread of the parasite is determined by the time it takes from hatching to the death of the copepodite. Furthermore the infestation window is determined by the longevity of survival for the copepodites. The purpose of the project was to measure larval developmental times at six temperatures representative for the Norwegian coast line. This information is crucial to understand the spread of the parasite and to estimate infection pressure created by gravid adult females on fish in the sea. All female salmon lice used had been acclimatized to the chosen temperature before intiation of the larval experiment. Hatching and survival was monitored in incubation trays in the laboratory. The main results were that the longest survival of copepodites, measured in days, was found at 7-10 °C. At 3 °C we did detect any production of copepodites, and at 5 °C the success of reinfection was significantly reduced . Salmon lice larvae had good survival even at the highest temperature (20 °C), but here survival was short, the animals small, and eggproduction decreased compared to the lower temperatures. These results provides new information about the performance of salmon louse at extreme temperatures and provide a useful tool in management of the parasite in aquaculture settings as well as in governmental management. Norsk: Utvikling og overlevelse av lakseluslarver (Lepeophtheirus salmonis) larver avhenger av temperatur. Spredningspotensialet bestemmes av tiden det tar å utvikle seg fra klekking av nauplier til kopepoditten dør. I tillegg er det smittsomme vinduet bestemt av hvor lenge kopepodittene overlever. Formålet med prosjektet var å måle utviklingstiden ved seks ulike temperaturer representative for hele den norske kystlinjen. Slike data er avgjørende for å forstå spredning av parasitten og å estimere smittepresset skapt av gravide voksne holus på fisk i sjøen. Alle moderlus ble akklimatisert til den valgte temperaturen før oppstart av larveeksperimentet. Klekking og overlevelse ble overvåket i inkubatorer i laboratoriet. Resultatet av forsøkene er at den lengste overlevelsen av infestiøse larver, målt i døgn, ble funnet ved 7-10 °C. Ved 3 °C fant vi ingen produksjon av kopepoditter og infeksjonssuksessen var sterkt redusert ved 5 °C. Lakseluslarvene overlevde selv ved den høyeste temperaturen (20 °C), men her var levetiden deres kortere, dyrene mindre og eggproduksjonen redusert. Resultatene gir ny informasjon om utviklingshastigheter av lakselus, spesielt ved høye og lave temperaturer. Dataene er viktig for å gi mer presisjon i verktøykassen for håndtering av parasitten i akvakultur så vel som i forvaltning

The effect of different intensities of the ectoparasitic salmon lice (Lepeophtheirus salmonis) on Atlantic salmon (Salmo salar)

The effect of different intensities of the ectoparasitic salmon lice (Lepeophtheirus salmonis) on stress, growth and the expression of immune and wound healing transcripts in the skin of Atlantic salmon (Salmo salar) was investigated. Lice infection success and survival were similar at the chalimus and preadult stage in the low and high dose group, but infection success and survival were significantly lower in the high than in the low dose group at the adult stage. The expression of investigated transcripts was not correlated to lice intensities, but several of them were significantly differently expressed locally in the skin at the site of lice attachment in infected fish compared to controls. This included an up-regulation of pro-inflammatory markers at the site of lice attachment (e.g., interleukin 1-beta, interleukin 8 and the acute phase protein serum amyloid A), a reduction of markers of adaptive immunity (cluster of differentiation 8-alpha and immunoglobulin M) and decreased expression of the anti-inflammatory cytokine interleukin 10.publishedVersio

Utvikling av lakselus ved ulik temperatur og lys - TEMPLUS

Lakselus påvirkes sterkt av miljøfaktorer som sjøvannets temperatur og saltholdighet. Sjøvannstemperaturen langs varierer sterkt avhengig av sesong og geografisk plassering. Saltholdighet utviser også store forskjeller lokalt, spesielt i fjorder med stort innslag av ferskvann. Formålet med dette prosjektet var å a) undersøke temperaturens innflytelse på utviklingsprosesser i lakselus på fisk og b) undersøke innflytelsen av saltholdighet og temperatur på adferden til frittlevende larvestadier. Alle forsøk ble utført i kar med lakselus samlet fra vestkysten av Norge. Resultatene viser tydelig at temperaturen er en sterk regulator av alle undersøkte biologiske prosesser i lakselus, med raskere utvikling, høyere reproduksjon og større infeksjonssuksess funnet ved høye temperaturer. Både saltholdighet og temperatur har også stor innflytelse på larveadferd, med forskjellige effekt på naupliuslarver og de smittsomme kopepoditter. Resultatene som er oppnådd, kan brukes til å predikere utvikling av lakselus i akvakultur og i laboratoriet, og gi ny informasjon om forvaltningen av parasitten ved lave temperaturer. Resultatene på larveadferd vil forbedre modellering av smittsomme kopepoditter og hjelpemiddel i utforming og bruk av forebyggende tiltak som brukes i oppdrettsanlegg.publishedVersio

Effects of chitin synthesis inhibitor treatment on Lepeophtheirus salmonis (Copepoda, Caligidae) larvae

The salmon louse (Lepeophtheirus salmonis) is an ectoparasite infecting Atlantic salmon (Salmo salar), which causes substantial problems to the salmon aquaculture and threatens wild salmon. Chitin synthesis inhibitors (CSIs) are used to control L. salmonis in aquaculture. CSIs act by interfering with chitin formation and molting. In the present study, we investigated the action of four CSIs: diflubenzuron (DFB), hexaflumuron (HX), lufenuron (LF), and teflubenzuron (TFB) on larval molt. As the mode of action of CSIs remains unknown, we selected key enzymes in chitin metabolism and investigated if CSI treatment influenced the transcriptional level of these genes. All four CSIs interfered with the nauplius II molt to copepodids in a dose-dependent manner. The EC50 values were 93.2 nM for diflubenzuron, 1.2 nM for hexaflumuron, 22.4 nM for lufenuron, and 11.7 nM for teflubenzuron. Of the investigated genes, only the transcriptional level of L. salmonis chitin synthase 1 decreased significantly in hexaflumuron and diflubenzuron-treated larvae. All the tested CSIs affected the molt of nauplius II L. salmonis larvae but at different concentrations. The larvae were most sensitive to hexaflumuron and less sensitive to diflubenzuron. None of the CSIs applied had a strong impact on the transcriptional level of chitin synthesis or chitinases genes in L. salmonis. Further research is necessary to get more knowledge of the nature of the inhibition of CSI and may require methods such as studies of protein structure and enzymological studies.publishedVersio

Sluttrapport for INFEST - Effekter av infestasjonsparametere på interaksjonen mellom laks og lakselus

Lakselus er per dags dato en av de største utfordringene i norsk og internasjonalt lakseoppdrett. Langsiktige løsninger for å begrense infestasjoner er nødvendig for å opprettholde en bærekraftig industri. Lakselusen er en ektoparasitt som sitter på huden av vertsfisken og kontakten mellom immunsystemet til verten og parasitt er derfor begrenset. Atlantiske laksefisk (Laks, sjøørret og sjørøye) er mottakelige for gjentakende infestasjoner med parasitten. Prosjektet har studert interaksjonen mellom lakselus og Atlantisk laks med spesielt søkelys på det immunologiske svaret i laksehud hvor lakselusen sitter. Denne immunologiske responsen var karakterisert ved bruk av gen ekspresjonsanalyse og forsøkene belyste hvordan infestasjonsforhold som temperatur, smittepress og infestasjonsmønster påvirkede denne responsen. Genuttrykk i laksen viste de største forandringer i huden rett under hvor lus var plassert. Høye temperaturer var positive for laksen sin evne til å reagere på infestasjonen, mens antallet av lakselus hadde lite betydning. Den immunologiske responsen på gjentatt infestasjoner var kompleks og knyttet opp imot antallet av lakselus, lengde av infestasjon og stress i fisken. Basale biologiske studier av samspillet mellom lakselus og fisken er viktig verktøy for å kunne håndtere og begrense lakselusinfestasjoner i fremtiden.publishedVersio

Chitin synthases are critical for reproduction, molting, and digestion in the salmon louse (Lepeophtheirus salmonis)

Chitin synthase (CHS) is a large transmembrane enzyme that polymerizes Uridine diphosphate N-acetylglucosamine into chitin. The genomes of insects often encode two chitin synthases, CHS1 and CHS2. Their functional roles have been investigated in several insects: CHS1 is mainly responsible for synthesizing chitin in the cuticle and CHS2 in the midgut. Lepeophtheirus salmonis is an ectoparasitic copepod on salmonid fish, which causes significant economic losses in aquaculture. In the present study, the tissue-specific localization, expression, and functional role of L. salmonis chitin synthases, LsCHS1 and LsCHS2, were investigated. The expressions of LsCHS1 and LsCHS2 were found in oocytes, ovaries, intestine, and integument. Wheat germ agglutinin (WGA) chitin staining signals were detected in ovaries, oocytes, intestine, cuticle, and intestine in adult female L. salmonis. The functional roles of the LsCHSs were investigated using RNA interference (RNAi) to silence the expression of LsCHS1 and LsCHS2. Knockdown of LsCHS1 in pre-adult I lice resulted in lethal phenotypes with cuticle deformation and deformation of ovaries and oocytes in adult lice. RNAi knockdown of LsCHS2 in adult female L. salmonis affected digestion, damaged the gut microvilli, reduced muscular tissues around the gut, and affected offspring. The results demonstrate that both LsCHS1 and LsCHS2 are important for the survival and reproduction in L. salmonis.publishedVersio

Temperature affects settlement success of ectoparasitic salmon lice (Lepeophtheirus salmonis) and impacts the immune and stress response of Atlantic salmon (Salmo salar)

In this study, the effect of temperature on Atlantic salmon (Salmo salar) stress and immune response to the ectoparasitic salmon lice (Lepeophtheirus salmonis) was investigated. We found that infestation affected the expression of several immune and wound healing transcripts in the skin especially at the site of lice attachment compared to un-infested control fish. Moreover, expression patterns in the skin of infested fish suggest that host immune responses towards salmon lice are impaired at low temperatures. However, reduced lice infestation success and survival at the lowest investigated temperatures suggest that cold water temperatures are more detrimental to the lice than their fish hosts. Finally, temperature affected the stress response of the fish and infected fish had a higher increase in cortisol levels in response to handling (a stressor) than un-infested controls.publishedVersio

Microsomal triglyceride transfer protein in the ectoparasitic crustacean salmon louse (Lepeophtheirus salmonis)

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Two apolipoproteins in salmon louse (Lepeophtheirus salmonis), apolipoprotein 1 knock down reduces reproductive capacity

The salmon louse, Lepeophtheirus salmonis is an ectoparasite of salmonid fish in the Northern Hemisphere, causing large economical losses in the aquaculture industry and represent a threat to wild populations of salmonids. Like other oviparous animals, it is likely that female lice use lipoproteins for lipid transport to maturing oocytes and other organs of the body. As an important component of lipoproteins, apolipoproteins play a vital role in the transport of lipids through biosynthesis of lipoproteins. Apolipoproteins have been studied in detail in different organisms, but no studies have been done in salmon lice. Two apolipoprotein encoding genes (LsLp1 and LsLp2) were identified in the salmon lice genome. Transcriptional analysis revealed both genes to be expressed at all stages from larvae to adult with some variation, LsLp1 generally higher than LsLp2 and both at their highest levels in adult stages of the louse. In adult female louse, the LsLp1 and LsLp2 transcripts were found in the sub-epidermal tissue and the intestine. RNA interference-mediated knockdown of LsLp1 and LsLp2 in female lice resulted in reduced expression of both transcripts. LsLp1 knockdown female lice produced significantly less offspring than control lice, while knockdown of LsLp2 in female lice caused no reduction in the number of offspring. These results suggest that LsLp1 has an important role in reproduction in female salmon lice.publishedVersio