Alterations of dopaminergic and serotonergic activity in the brain of sea‐run Baltic salmon suffering a thiamine deficiency‐related disorder

Baltic salmon Salmo salar females displaying wiggling behaviour had significantly lower (P<0.05) hepatic and ovarian thiamine (vitamin B 1 ) concentrations than the normal females, confirming that they suffered from a thiamine deficiency. A significantly (P<0.05) increased monoaminergic activity was found in the telencephalon and the hypothalamus of the wiggling individuals as indicated by [5‐hydroxyindoleacetic acid (5‐HIAA)]: [5‐hydroxytryptamine (5‐HT)] and [3,4‐dihydroxyphenylacetic acid (DOPAC)]: [dopamine (DA)] ratios. The 5‐HIAA concentrations of wiggling individuals were significantly (P<0.05) higher in the telencephalon and the hypothalamus compared to normal fish. Wiggling fish showed significantly (P<0.05) higher concentrations of the DA metabolite DOPAC in the hypothalamus and the brain stem compared to normal fish. Furthermore, the brain stem in wiggling fish contained significantly (P<0.05) less 5‐HT than in normal individuals, which was also reflected in a significant (P<0.05) increase in the (5‐HIAA): (5‐HT) ratio. These results demonstrate an increased serotonergic and dopaminergic activity in wiggling compared to normal fish. The altered monoaminergic activity may be directly related to altered brain thiamine metabolism, but a general stress caused by thiamine deficiency and an inability to regulate swim bladder inflation may contribute. Furthermore, a changed brain monoaminergic activity may contribute to the behaviour characterizing wiggling fish.