Influence of lipids and fatty acid composition on Baltic cod (Gadus morhua) maturation and timing of spawning

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The Baltic Sea experienced an ecosystem regime shift in the late 1980ies with great changes in food web dynamics and a decrease of the Eastern Baltic cod stock biomass to a historically low level in 1992. This decline was caused by high fishing pressure combined with a recruitment failure (Köster et al. 2003; Möllmann et al. 2008). In addition, the main spawning time of Eastern Baltic cod shifted from April-June to July-August in the early 1990ies. Effects of temperature and demographic changes in the cod stock do not fully explain this shift (Wieland et al. 2000). However, also the prey composition and condition of sprat and herring being the main prey of Baltic cod changed during this period influencing cod dietary lipid intake. As cod uses liver lipid stores for reproduction changed lipid intake or deficiency of essential fatty acids (EFA) could influence ovarian development and thereby the spawning time.