Novel Scale Chemistry of Salmo Salar L. : New Linkage of Otolith and Scale Chemistry to M74 Reproductive Disorder

Sammanfattning: Baltic salmon suffer from maternally transmitted M74 reproductive disorder, which causes yolk-sac fry mortality due to thiamine deficiency. This study investigates trace elemental analyses of Baltic salmon applied on otoliths and scales and their possible link to identifying M74. Using laser-ablated inductively coupled plasma mass spectrometry, 170 female salmon from two Swedish rivers were chemically analysed. Egg thiamine concentrations were measured using chromatography. This study shows that novel scale chemistry aligns with traditional otolith chemistry regarding salmons’ environmental and physiological patterns. Comparison between two chemical age-readers, using Mg:Ca, found 73% and 70% agreement for otoliths and scales, respectively. Comparing both structures revealed 51 – 58% agreement precision between both readers. Different degrees of vaterite formation were found in 48% of included otoliths but were not significantly correlated to M74. The chemical analyses mirrored trace elemental patterns reflecting salinity (Sr:Ca) and fresh- and saltwater transition (Ba:Ca) in both structures, revealing that scale chemistry can be used for migration studies. The Sr:Ba ratio in scales from severely thiamine deficient salmon (thiamine concentration < 0.4 nmol/g) showed significantly lower mean levels than healthier fish (> 8 nmol/g) throughout the whole life cycle, indicating that severely deficient salmon use coastal habitats more than healthier fish. The Sr:Ba ratio in scales correlated negatively to trace elements known for tracking pollution (Pb, U, Zn, and Cu). Additionally, a significant increase of B over life in the otoliths of severely deficient fish was discovered. Scale Sr:Ba shows novel promising results as a non-lethal sampling alternative for tracking M74 in Baltic salmon, with potential as a biomarker already early in life.