Influence of long term ammonia exposure on Atlantic salmon (Salmo salar L.) parr growth and welfare

Abstract

AbstractThe objective of this study was to determine thelong-term effects of ambient unionized ammonianitrogen (NH 3 -N) combined with different feedingregimes on Atlantic salmon Salmo salar L parrgrowth, welfare and smoltification. Previous stud-ies on the parr stage of Atlantic salmon havemostly focused on acute exposure, or at lowtemperatures. Atlantic salmon parr were exposedfor 105 days (at 12°C, pH 6.8) to four sublethalammonia concentrations ranging from 0.1 to35 lgL 1 NH 3 -N (0.1–25 mg L 1 TAN) at twofeeding levels: full feed strength (+20% overfeed-ing) and 1/3 of full feed strength. After 21 days,it was observed that 32 lgL 1 NH 3 -N reducedgrowth rate of parr fed full ration, but this effectwas not evident at the end of the exposure. Feedutilization was not affected by ammonia expo-sure at any sampling point. Increasing ammonialevels were associated with a higher prevalenceand severity of gill damage at 22 days but notat the end of the exposure. The examination ofwelfare indicators revealed only a few patholo-gies, not related to ammonia exposure. In addi-tion, higher ammonia concentrations did notappear to influence the development of hypo-osmoregulatory ability during parr-smolt transfor-mation.Keywords: ammonia exposure, Atlantic salmon,growth, welfare, gill histology, smoltificationIntroductionAmmonia is the main nitrogenous waste product inmost teleosts and it is mainly excreted through gillsto the surrounding water (Randall & Wright 1987;Fivelstad, Kellevik, Iversen, Moretro, Va˚ge & Binde1993; Randall & Tsui 2002; Wilkie 2002; Eddy2005). Ammonia is a toxicant with negative effectson teleosts dependent on e.g. the species, develop-mental stage, feeding rate, swimming activity andother factors (Wright & Fyhn 2001; Finn 2007; Ter-jesen 2008). In intensive high-density flow-throughsystems ammonia build-up can cause reducedgrowth and mortality (Person-Le Ruyet, Galland, LeRoux & Chartois 1997). In water, total ammoniaexists asthesum oftheun-ionized (NH