Fatty acid composition of sprat (Sprattus sprattus) and herring (Clupea harengus) in the Baltic Sea as potential prey for salmon (Salmo salar)

Abstract

Sprat (Sprattus sprattus) and small herring (Clupea harengus) are the dominant prey fish of Atlantic salmon (Salmo salar) in the Baltic Sea. If the fatty acid (FA) proportions of sprat and herring differ, the dietary history of ascending salmon could be determined from their FA profiles. Therefore, we investigated the FA composition of several age groups of whole sprat and small herring, caught from the three main feeding areas of salmon in autumn and spring. Oleic acid (18:1n-9) was the most prevalent FA in sprat and characteristic of this species. In herring, palmitic acid (16:0) was the most common FA, but herring lipid was characterized by n-6 polyunsaturated FAs, and moreover, by palmitoleic acid (16:1n-7) and vaccenic acid (18:1n-7). Due to the higher lipid content of sprat, the concentrations of all other FAs, excluding these, were higher in sprat than in herring. The concentration of docosahexaenoic acid (DHA, 22:6n-3) increased with an increase in the lipid content and was consequently highest in the youngest specimens, being in young sprat almost double that of young herring, and 2.6 times higher in the sprat biomass than in that of herring. As a result of a decrease in the DHA concentration with age, the ratio thiamine/DHA increased with respect to age in both species, and was lower in sprat than in herring. It is concluded that an abundance of DHA in the diet of salmon most likely increases oxidative stress because of the susceptibility of DHA to peroxidation, and thus decreases thiamine resources of fasting, prespawning salmon. Because the FA composition of sprat and herring differs, and the relative abundancies of prey fish differ between the feeding areas of salmon, the feeding area of ascending salmon can most probably be derived by comparing their FA profiles.

Influence of the marine feeding area on the muscle and egg fatty‐acid composition of Atlantic salmon Salmo salar spawners estimated from the scale stable isotopes

“…1·0–0·9% for muscle and c . 1·7–1·5% for eggs) in studied S. salar , but a low proportion was equally observed in its main prey species (Røjbek et al ., ; Keinänen et al ., in press). Thus, dietary resources in the final feeding area of spawning S. salar were reflected in these PUFA in their total lipids and ARA was the best resulting indicator from the final probable feeding area characteristics.…”

“…Condition factors of S. salar were roughly similar to those reported previously from spawning S. salar (Mikkonen et al ., ; Vuorinen et al ., ), although higher condition factors were observed in years of high M74 incidence in pre‐spawning S. salar that evidently had returned from the Baltic Sea proper (Mikkonen et al ., ). The M74 syndrome has caused variable and occasionally very high, mortality during the yolk‐sac fry phase of offspring from those female S. salar (Keinänen et al ., , in press). The M74 syndrome is especially related to the abundance of young S. sprattus in the Baltic Sea proper having the highest lipid content and therefore also a high unsaturated FA content (Karlsson et al ., 1999; Keinänen et al ., ).…”

Factors affecting the degree of vertical stratification of fatty acids in grey seal blubber

“…The average levels of the longer chain and more highly unsaturated FAs remained unchanged through the depth of the blubber (except 20:5n-3, which was less abundant in the outer blubber than in the other layers). Since the lipids of the prey in the Baltic Sea are not especially rich in MUFAs but the PUFAs and SFAs dominate (Keinänen et al 2017;Tverin et al 2019), the high MUFA contents of the outer blubber of the seal can be seen as an adaptive response to the varying and cooler tissue temperature of outer blubber. The MUFA enrichment in Hyvärinen 1996, andStrandberg et al 2008, and used as reference with full permission from the authors).…”

Deficiency syndromes in top predators associated with large-scale changes in the Baltic Sea ecosystem

“…Large numbers of wild animals from a wide range of taxonomic groups in several ecosystems show signs of vitamin B 1 (thiamin or thiamine) deficiency [1][2][3][4][5][6][7]. In addition to mortality, thiamin deficiency can also result in compromised health, altered behavior and reproductive failure, thus potentially leading to population decline [4,[8][9][10]. Thiamin is a crucial micronutrient for all organisms and has various central cellular functions (for a review, see Kraft and Angert [11]).…”

“…In the Baltic Sea, this species displays year-to-year fluctuations in the incidence of a thiamin deficiency syndrome called M74, which is reported as the proportion of females producing offspring with M74. M74 leads to offspring mortality during the yolk-sac fry stage [1,6,7,9,12], and as many as 70-80% of the females produce offspring with the syndrome in some years, leading to nearly 100% mortality in the offspring [13]. Salmon with thiamin deficiency typically exhibit discoloration of the skin and internal organs and neurological symptoms [1,14].…”