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In 2023, exceptionally few salmon (Salmo salar) ascended from the Baltic Sea to spawn in the Rivers Tornionjoki and Simojoki, regardless of the proper number of smolts descending to the sea in preceding years. We investigated how the numbers of age-0 and young herring (Clupea harengus) and sprat (Sprattus sprattus), which are the principal prey species of salmon in the Baltic Proper, the main feeding area of these salmon, as well as the amount of lipid obtained from them and their protein-to-lipid ratio, correlated with the number of returning salmon and the thiamine (vitamin B1) status of spawning salmon. The fewer the 0-year-old herring were and the more abundant were the youngish sprat in the Baltic Proper when the post-smolts arrived there, and the greater the lipid content and lower the protein-to-lipid ratio of the prey fish, the fewer salmon returned to the Rivers Tornionjoki and Simojoki to spawn two years later. The number of returning salmon was lowest with a high ratio of youngish sprat, 1–3 years old, regarding the River Tornionjoki and 1–2 years old regarding the River Simojoki post-smolts, to 0-year-old herring, which were of a suitable size to be the prey for the post-smolts upon their arrival in the Baltic Proper. In 2021, the ratios were lowest due to the record-low number of 0-year-old herring. The poor thiamine status of spawning salmon was also associated with the high lipid content of available prey fish and with the abundance of youngish sprat, which have twice the lipid content of age-0 herring. Our findings parallel the observations in the early 1990s when post-smolt survival declined concurrently with the outbreak of thiamine deficiency, M74. We conclude that consuming high-lipid marine fish reduces the survival of post-smolts and, thus, the number of returning salmon, in addition to causing thiamine deficiency. [ABSTRACT FROM AUTHOR]

Lipid-related thiamine (vitamin B1) deficiency of Baltic salmon (Salmo salar), the M74 syndrome, is generally caused by feeding on abundant young sprat (Sprattus sprattus) in the Baltic Proper, the main foraging area of these salmon. In 2014, a strong year-class of sprat was hatched in the Baltic Proper, and a strong herring (Clupea harengus) year-class was hatched in the Gulf of Bothnia, where herring is the dominant salmon prey. The fatty acid (FA) signatures of prey fish in muscle or eggs of second sea-year spawners suggested that 27% of wild River Simojoki and 68% of reared River Dal salmon remained in the Gulf of Bothnia in 2014 instead of continuing to the Baltic Proper. In 2016, 23% of the M74 females of the River Simojoki and 58% of the River Dal originated from the Gulf of Bothnia, and 13% and 16%, respectively, originated from the Baltic Proper. Some salmon from the River Neris in the southern Baltic Proper had also been feeding in the Gulf of Bothnia. In general, low free thiamine (THIAM) concentration in eggs was associated with high lipid content and high docosahexaenoic acid (DHA, 22:6n−3) and n−3 polyunsaturated FA (n−3 PUFA) concentrations in muscle but not in eggs. A higher THIAM concentration and lower proportions of DHA and n−3 PUFAs in Arctic Ocean salmon eggs, despite higher egg lipid content, indicated that their diet contained fewer fatty fish than the Baltic salmon diet. Hence, M74 originated by foraging heavily on young fatty sprat in the Baltic Proper or herring in the Gulf of Bothnia. [ABSTRACT FROM AUTHOR]

Atlantic salmon (Salmo salar) collected from three locations around the northern Baltic Sea in 2003-2004 showed large spatial and individual variation in their organochlorines (OCs) (polychlorinated dibenzo-p-dioxins and furans and polychlorinated biphenyls). This variation could be explained only partly by their size or sea age. The variability arose from the differences in salmon diet, trophic position, and prey OC concentrations and lipid content. A salmon bioenergetics accumulation model was used to evaluate the contribution of salmon growth and their diet to the observed individual variation in OC content. Our model revealed that the contribution of three main prey species in the OC accumulation of salmon varied markedly between the study areas. Amount of lipids in salmon explained a large proportion of their OC concentration. However, trophic position of salmon calculated from the [delta][sup.15]N values explained almost 80% of the variation in lipid-normalized OC concentrations. In the Gulf of Finland, where OC concentrations of salmon were highest, their prey species had the highest OC concentrations and trophic positions. Higher OC concentrations in the Gulf of Finland might be related to elevated trophic positions caused by invasion of the predatory cladoceran Cercopagis pengoi in 1990. Des saumons (Salmo salar) recoltes a trois sites autour du nord de la Baltique en 2003-2004 affichent d'importantes variations spatiales et individuelles de leurs concentrations de composes organochlores (OC; dibenzo-p-dioxines polychlorees et furanes et biphenyles polychlores). La taille des poissons et le temps passe en mer n'expliquent que partiellement cette variation. La variabilite provient de differences dans le regime alimentaire et la position trophique des saumons, de meme que des concentrations d'OC et de lipides de leurs proies. Un modele bioenergetique d'accumulation chez le saumon a servi a evaluer la contribution de la croissance et du regime alimentaire des saumons a la variation individuelle d'OC observee. Notre modele revele que les contributions des trois especes principales de proies a l'accumulation d'OC chez les saumons varient considerablement d'une zone d'etude a l'autre. La quantite de lipides chez les saumons explique une proportion importante de leur concentration d'OC. Cependant, la position trophique des saumons calculee d'apres les valeurs de [delta][sup.15]N explique presque 80 % de la variation des concentrations normalisees d'OC dans les lipides. Dans le golfe de Finlande ou les concentrations d'OC chez les saumons sont les plus grandes, les especes de proies possedent les concentrations d'OC les plus fortes et occupent la position trophique la plus elevee. Les concentrations plus eleve es d'OC dans le golfe de Finlande peuvent etre relies a des positions trophiques superieures resultant de l'invasion du cladocere predateur Cercopagis pengoi en 1990. [Traduit par la Redaction], Introduction Baltic Sea fish, in general, possess very high concentrations of organochlorine compounds (OCs), such as polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and polychlorinated biphenyls (PCBs). PCDD/F and PCB concentrations in [...]

Abstract: The Baltic Sea is exposed to severe human impacts. Besides eutrophication and overfishing, a variety of chemical contaminants threaten the health of fish. During a cruise in December 2001, [...]

The impact of the individual fish variability and fisheries management on the extent of the human dietary intake of organochlorines from the Northern Baltic herring was studied. The analysis suggests that regulating the consumption of herring is more effective in the risk management of such organochlorines, as compared to the regulation of fishing.

Abstract: In this paper, we demonstrate how information from broodstocks can be combined with lab information on alevins to obtain annual stock-specific mortality estimates from early mortality syndromes (EMS) using [...]

Signs of impaired thiamine (vitamin B1) status in feeding-migrating Atlantic salmon (Salmo salar) were studied in three Baltic Sea areas, which differ in the proportion and nutritional composition of prey fish sprat (Sprattus sprattus) and herring (Clupea harengus). The concentration of n−3 polyunsaturated fatty acids (n−3 PUFAs) increased in salmon with dietary lipids and n−3 PUFAs, and the hepatic peroxidation product malondialdehyde (MDA) concentration increased exponentially with increasing n−3 PUFA and docosahexaenoic acid (DHA, 22:6n−3) concentration, whereas hepatic total thiamine concentration, a sensitive indicator of thiamine status, decreased with the increase in both body lipid and n−3 PUFA or DHA concentration. The hepatic glucose 6-phosphate dehydrogenase activity was suppressed by high dietary lipids. In salmon muscle and in prey fish, the proportion of thiamine pyrophosphate increased, and that of free thiamine decreased, with increasing body lipid content or PUFAs, or merely DHA. The thiamine status of salmon was impaired mainly due to the peroxidation of n−3 PUFAs, whereas lipids as a source of metabolic energy had less effect. Organochlorines or general oxidative stress did not affect the thiamine status. The amount of lipids, and, specifically, their long-chain n−3 PUFAs, are thus responsible for generating thiamine deficiency, and not a prey fish species per se. [ABSTRACT FROM AUTHOR]

Abstract Background We have studied alterations of gene expression associated with naturally-occurring early life stage mortality (M74) in Baltic salmon using a cDNA microarray and real time PCR. M74-affected fry have several typical neurological, cardiovascular and pathological symptoms. They are also characterized by low thiamine content and show signs of oxidative stress. Results Affected fry can be divided into three major groups with early, intermediate or late onset of mortality. If mortality starts during the first third of the yolk-sac stage, virtually all the responses are compatible with stress, which rapidly leads to the common terminal responses. If death occurs during the second third of the yolk sac stage, the terminal stage is preceded by a decrease in globin gene expression, which leads to internal hypoxia when the animals grow and shift from skin- to gill-breathing. Fry will eventually proceed to the terminal responses. The group developing M74 most slowly appears to compensate for reduced oxygen delivery by downregulation of metabolism, and hence some fry can escape death. Conclusion Our study is the first demonstration of diverse transcriptional responses to a naturally-occurring developmental disturbance. Since many of the genes differentially expressed in M74-fry are evolutionarily conserved, the M74 of Baltic salmon can serve as a model for developmental disturbances and environmental stress responses in vertebrates in general.

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. [ABSTRACT FROM AUTHOR]