No environmental effect on vaccine-induced reduced growth in Atlantic salmon Salmo salar smolts

V Heen,Twk Fraser,T Søfteland,O Høstmark,Md Powell,I Sommerset,Pg Fjelldal,Tj Hansen

doi:10.3354/aei00367

Abstract

Oil-adjuvanted vaccines reduce long-term growth in farmed Atlantic salmon Salmo salar, possibly via an increase in metabolic rate due to the energetic demands of the immune system. We tested this hypothesis by comparing sham-vaccinated to vaccinated smolts (total n = 2096, ca. 80 g) under different scenarios of water temperature (12 vs. 17°C, n = 1048 per temperature) and oxygen (O2) saturation (60, 70, 80, and 100%, n = 524 per O2 saturation level) in order to manipulate metabolic rate and O2 availability. We expected a more severe vaccination effect under conditions of high water temperature and low O2 saturation. Groups were kept in duplicate tanks under controlled temperature and hypoxia conditions for 7 wk post-vaccination before being transferred to uncontrolled common-garden natural conditions for 5 mo in a sea-cage. Body mass and length were recorded at the initiation and end of the controlled and uncontrolled environmental conditions. Vaccination and low O2 saturation at 17°C significantly reduced body mass (13 and 3% through vaccination and 9 and 20% through 60% O2 saturation at the end of the tank and sea-cage periods, respectively). However, there was no interaction between vaccination, temperature, and O2 saturation at the end of the tank or sea-cage period, lending no support to our hypothesis. A secondary observation was that emaciated ‘loser’ fish were mainly associated with the 17°C and low (mainly 60%) O2 saturation treatment. In conclusion, although vaccination led to a reduction in body mass, this effect was not influenced by environmental conditions expected to alter metabolic rate.

Highlights

Salmon farming in Norway relies on the protection provided by multi-component vaccines, and this has contributed both to the growth of the industry and its relatively low level of antibiotic use compared to other salmon farming regions (Love et al 2020).oil-adjuvanted vaccines induce abdominal lesions and peritonitis (Midtlyng et al 1996), lead to short-term reductions in feed intake (Sørum & Damsgård 2004), and reduce growth by between 9 and 23% post-vaccination (Midtlyng & Lilllehaug 1998, Fraser et al 2014)
We report on the long-term effects of the environmental conditions and vaccination on growth and production characteristics (antibody production, ‘loser’ fish, post-smolt maturation, cataracts, radiological deformities) during 5 mo of common garden rearing in a sea-cage
We investigated whether growth following vaccination was associated with environmental conditions expected to alter or limit metabolic rate and found no support for our hypothesis that vaccination leads to an increase in metabolic demand, resulting in reduced growth

Summary

Introduction

Oil-adjuvanted vaccines induce abdominal lesions and peritonitis (Midtlyng et al 1996), lead to short-term reductions in feed intake (Sørum & Damsgård 2004), and reduce growth by between 9 and 23% post-vaccination (Midtlyng & Lilllehaug 1998, Fraser et al 2014). As oil-adjuvanted salmon vaccines lead to a chronically active immune response that peaks at 6 mo post-vaccination (Mutoloki et al 2004, 2006), one may suspect that the reduced growth is a result of an increased metabolic cost of the immune system. Fraser et al (2015) observed an increase in heart size in vaccinated vs unvaccinated fish, which is suggestive of an increase in cardiac workload that one may expect with an increase in metabolic demand. As factorial aerobic scope is known to be reduced with increasing environmental temperature in salmon (Hvas et al 2017), one may speculate that higher than optimal temperatures may reduce the amount of energy available to the immune system that is expected to be energy-demanding (Lochmiller & Deerenberg 2000)

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