Abstract
Thiamine (vitamin B1) deficiency in salmonids related to a lipid-rich fish diet causes offspring mortality in the yolk-sac fry phase. A low free thiamine (THIAM) concentration in eggs is an indication of this syndrome. Thiamine deficiency of salmon (Salmo salar) feeding in the Baltic Sea, called M74, was connected to the principal prey fish and feeding area using fatty acid (FA) signature analysis. The FAs of feeding salmon from two areas of the Baltic Sea, the Baltic Proper (57°10′ 19°30′) and the Bothnian Sea (61°30′ 20°00′) in 2004, reflected the principal prey species in these areas, sprat (Sprattus sprattus) and herring (Clupea harengus), respectively. Arachidonic acid (ARA, 20:4n-6) and 18:1n-7 indicated dietary herring, 18:1n-9 dietary sprat and 14:0 feeding in the Baltic Proper. The muscle FA profile of non-M74 female spawners of the River Simojoki in a year (1998) with a moderate M74 incidence and salmon of a non-M74 year (2004) reflected herring FAs, whereas the FAs in the M74 year and specifically in M74 females displayed characteristics of sprat. In the M74 year, the THIAM concentration had the strongest positive correlation with the proportion of muscle ARA, and the strongest negative correlations with 14:0 and the ratios 18:1n-9/ARA and 14:0/ARA. Thus, ARA along with 14:0 and these ratios were the most sensitive FA indicators of the dietary species and origin of the M74 syndrome. Despite the pre-spawning fasting, tissue FA signatures were consequently able to connect dietary sprat in the Baltic Proper with thiamine deficiency in Baltic salmon.
Highlights
Thiamine deficiency disturbing the reproduction of Atlantic salmon (Salmo salar) feeding in the Baltic Sea is known as the M74 syndrome (Bengtsson et al 1999)
The fatty acid (FA) signature of the diet is manifested in the muscle of spawning salmon, despite the extensive lipid metabolism and subsequent FA mobilisation during the pre-spawning fasting and oocyte development
The most sensitive indicators of the main prey fish of Baltic salmon are ARA and the ratio 18:1n-9/ARA, since the lipid of sprat is characterised by 18:1n-9, whereas herring lipid is most clearly characterised by ARA among n-6 polyunsaturated FA (PUFA)
Summary
Thiamine (vitamin B1) deficiency disturbing the reproduction of Atlantic salmon (Salmo salar) feeding in the Baltic Sea (hereafter salmon or Baltic salmon) is known as the M74 syndrome (Bengtsson et al 1999). M74 has been connected to a lipid-rich diet, and one including young sprat (Sprattus sprattus) with a high lipid content (Karlsson et al 1999a; Mikkonen et al 2011; Keinänen et al 2012). Another important prey fish of Baltic salmon is the herring (Clupea harengus), of which salmon prefer smaller specimens (Hansson et al 2001; Vuorinen et al 2014a). The concentration of astaxanthin and the total concentration of carotenoids are on average
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