Model for estimating thiamine deficiency-related mortality of Atlantic salmon (Salmo salar) offspring and variation in the Baltic salmon M74 syndrome

Abstract

Thiamine (vitamin B1) deficiency of salmonines, caused by an abundant lipid-rich fish diet and consequently, the abundance of polyunsaturated fatty acids, is called the M74 syndrome in the Baltic Sea. Because of its deleterious effects on wild Atlantic salmon (Salmo salar) stocks and progeny production in fish cultivation, a model was developed to derive the annual female-specific mortality percentages of yolk-sac fry (YSFM) from the free thiamine concentrations of unfertilized eggs. In years with a high M74 incidence, thiamine-deficient females were larger, with a larger condition factor (CF) than non-M74 females. Otherwise, M74 females were generally smaller. The mean CF of M74 females was in most years higher than that of non-M74 females. The model compiled enables the cost-effective estimation of YSFM of individual female salmon, without the incubation of eggs and hatched yolk-sac fry for several months, thus benefitting the management of salmon stocks and their efficient utilization.

High Lipid Content of Prey Fish and n−3 PUFA Peroxidation Impair the Thiamine Status of Feeding-Migrating Atlantic Salmon (Salmo salar) and Is Reflected in Hepatic Biochemical Indices

“…Most Baltic salmon come from the rivers of the Gulf of Bothnia, the most important of which is the River Tornionjoki (Figure 1). At the beginning of the 1990s, thiamine (vitamin B1) deficiency syndrome M74 erupted abruptly among Baltic salmon, meaning that most offspring of salmon that had been feeding in the Baltic Sea died on fish farms, as well as in Finnish and Swedish salmon rivers in the 1990s for several years, and a variable proportion of the fry since then [3][4][5][6]. M74 endangered the wild salmon stocks of the Baltic Sea, which had already weakened due to heavy open sea fishing in the 1980s.…”

“…M74 endangered the wild salmon stocks of the Baltic Sea, which had already weakened due to heavy open sea fishing in the 1980s. Although Baltic salmon stocks approached extinction in the 1990s [7], e.g., the salmon stock of the River Tornionjoki has recovered because of strict fishing restrictions and large-scale and expensive recovery measures [4,8]. However, many stocks need to be artificially maintained and strengthened, for which 4.5 million smolts are annually produced by fish farms.…”

“…Thiamine deficiency particularly affects the offspring, which-during the embryonic and yolk-sac phases-must survive on the egg yolk nutrients provided by the brood female [3,12]. M74 and TDC symptoms, such as wriggling behavior and mortalities, have also been recorded among both sexes of ascended brood salmonines before and during the spawning period [4,[13][14][15][16]. The reason for the sudden increase in M74 at the turn of the 1980s and 1990s was the over-fishing of cod (Gadus morhua L.), the principal predator of sprat (Sprattus sprattus (L.)).…”

“…The proportion of salmon that remains to feed in the BS has depended on the smolt size and the strength of herring recruitment there; during 1986-2007, on average, approximately 14% of wild salmon smolts remained in the BS area annually instead of migrating to the BPr [45]. M74 also affects the salmon of the River Kymijoki, which flows into the Gulf of Finland (GoF, Figure 1) [4,8,46]. These salmon feed mainly in the GoF, where sprat has been more common than herring in recent decades [47,48].…”

“…The feeding area of this M74 female was also localized as being the BS, based on the ratio of PCDDs plus dibenzofurans (PCDD/Fs) to coplanar PCBs (CoPCBs) [2,52]. As the incidence of M74 is linked with the lipid and, therefore, also to the PUFA content of prey fish biomass [3,4,9,10], the abundant herring 2002 year class in the Gulf of Bothnia as prey [38] could have caused some M74 cases. Eating different foods could be detected by examining the dietary lipidrelated biochemical indices of salmon caught in 2004 from the three different feeding grounds in the Baltic Sea.…”