Vaccinated farmed Atlantic salmon are susceptible to spinal and skull deformities

Abstract

St Petersburg State University, St Petersburg,RussiaSummaryThe aim of this study was to investigate the effects ofvaccination, and starvation after vaccination, on the morphol-ogy of skull bones and vertebral bodies, bone mineralizationand the development of intra-muscular melanin deposits infarmed Atlantic salmon. For this purpose, triplicate groups ofvaccinated (V) or unvaccinated (UV) underyearling smolts(38 g) were fed normal rations (F), or starved for 3 weeks aftervaccination (S) (September 2004), leaving four experimentalgroups (V-F, V-S, UV-F, UV-S). After termination of thestarvation period, all groups were fed a normal ration until thefish reached a normal harvest size (January 2006). There wereno long term effects of starvation on body weight, bonemineralization or deformity incidence. However, at termina-tion, V fish (pooled mean V-F and V-S, 4.4 kg) were overallsignificantlysmallerthanUVfish(pooledmeanUV-FandUV-S, 5.1 kg), and they also developed overall significantly moredeformities in both the skull (pooled mean UV-F and UV-S27%,pooledmeanV-FandV-S81%)andthevertebralcolumn(pooledmeanUV-FandUV-S21%,pooledmeanV-FandV-S41%). These deformities were site-specific in both compart-ments; skull deformities were clearly observed in the ceratohy-ale anterior, while those in the vertebral column were mainlylocated in the tail region (V31–49). There were no significantcorrelations among individual relationships between the skulland vertebral column deformities. UV fish had overall signif-icantly higher vertebral bone total ash content than V fish attermination, butthere werenoeffectsonvaccinationontheashcontentor morphology ofthe vertebrae2 monthsafter transferto seawater. The incidences of intra-muscular melanin depositswere not significantly different between UV and V fish. Theseresults show that vaccination can induce deformities in thevertebral column and ⁄ or skull in farmed Atlantic salmon. Thesite-specificlocationofthedeformitiesinrelationtomechanicalloading is discussed. Furthermore, the results show thatvaccination is not likely the main cause of the current melaninspot problem in Atlantic salmon aquaculture.IntroductionAll farmed Norwegian Atlantic salmon are vaccinated with oil-based adjuvant vaccines before they complete smoltification.This cause a short-term decrease in appetite (Sorum andDamsga˚rd, 2004), induces abdominal lesions that adhere andembed the visceral organs (Poppe and Breck, 1997; Midtlyng,1998) and may induce vertebral deformities (Berg et al., 2006a;Aunsmo et al., 2008), but also gives the fish protectiveimmunity against several diseases (Midtlyng et al., 1996a;Midtlyng, 1998; Lillehaug et al., 2003). Vaccination has alsobeen associated with muscle inflammation and melanin accu-mulation (Koppang et al., 2005), granulomatous uveitis(Koppang et al., 2004), and systemic autoimmunity (Koppanget al., 2008; Haugarvoll et al., 2010). Intra-muscular melanindeposits are a major problem in Atlantic salmon farming, butthe link with vaccination has never been studied. Themechanism behind vaccine induced vertebral deformities hasnot yet been identified. It is not clear whether the vaccine-induced deformities start to develop immediately after vacci-nation or later in the production cycle during on-growth inseawater. Small fish size at vaccination is identified as a riskfactor for vertebral deformities (Va˚gsholm and Djupvik, 1998;Berg et al., 2006a). Haugarvoll et al. (2010) suggest thatvaccine induced deformities can be coupled with systemicautoimmunity. Furthermore, low appetite combined withrelatively good growth in body length has been suggested toimpair bone mineralization and increase the risk for vertebraldeformities in Atlantic salmon (Fjelldal et al., 2007a; Griniet al., 2011). Hence, the short-term decrease in appetite aftervaccination (Sorum and Damsga˚rd, 2004), may make vacci-nated salmon prone to developing vertebral deformities.However, effects of a restricted ration or starvation onpathogenesis in the vertebral column in Atlantic salmon hasnever been tested. In addition, the presence of vaccine-inducedmalformations in other skeletal structures than the vertebralcolumn would indicate a link to a systemic autoimmune origin.The question of whether vaccination affects skeletal structuresother than the vertebral column has never been studied.This study examined the effects of vaccination and post-vaccination starvation on the development of deformities inthe skull and vertebral column. Triplicate groups of vaccinatedand un-vaccinated Atlantic salmon underyearling smolts werefed normal rations or starved for 3 weeks post-vaccination. Allgroups were thereafter fed a normal ration until harvest sizeand their growth performance, severity of abdominal lesions(lesion score), intra-muscular melanin deposits, malformationsin the vertebral column and skull, and mineralization of thevertebral bodies were measured.Materials and methods