EFFECTS OF VITAMIN B_1 (THIAMINE) DEFICIENCY IN LAKE TROUT (SALVELINUS NAMAYCUSH) ALEVINS AT HATCHING

摘要

Early mortality syndrome (EMS) has been described in salmonid populations in Lake Michigan and other Great Lakes as well as in Salmo solar and Gadus morhua in the Baltic Sea (M74 syndrome). It is associated with low concentrations of thiamine in eggsthat results in high mortality at yolksac and swim-up stages (Lundstrom et al. 1999). This effect in offspring has been linked to nutritional deficiencies, i.e. inadequate levels of thiamine in the diets of females (Fitzsimons, 1995; Brown et al., 2005).High levels of thiaminase have been found in prey species such as Alosapseudoharengus and Osmerus mordax. Laboratory experiments have revealed that 67% of lake trout families showed high incidence of EMS when free thiamine levels in eggs dropped below 0.8 nmol/g (Brown et al, 2005). Histopathological studies of yolksac alevins of Baltic salmon with M74 syndrome revealed an association between low thiamine concentrations in eggs and a wide spectra of pathological lesions observed in fish tissues (Lundstrom et al, 1999). The most recent studies on effects of thiamine deficiency in Salvelinus namaycush alevins at swim-up stage showed that in affected individuals all strata of the brain, olfactory nerve and eye retina contained necrotic neurons (Lee et al, 2008). The purpose of this study was to determine the association between newly hatched lake trout mortality and EMS in progenies of females from L. Michigan. Specifically, our aim was to examine the correlation between thiamine levels in unfertilizedeggs and then in the yolksac and tissues of embryos. We then wanted to establish criteria for individual fish (embryo at hatching) that would correlate pathological changes in the brain, eye and liver and thiamine concentration in the yolksac.