Cod reproductive ecology:Effect of dietary fatty acids on ovarian maturation, spawning time and quality of eggs and larvae
In recent decades, Baltic cod has experienced a period of low recruitment. In the same period the pelagic Baltic Sea ecosystem experienced a regime shift, due to hydrographic changes, affecting all trophic levels. The rationale for the thesis is built on the hypothesis that the regime shift has resu...
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| Format: | Book |
| Language: | English |
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DTU Aqua
2012
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| Online Access: | https://orbit.dtu.dk/en/publications/91ae5037-1730-4c4d-aba9-ebe4c01a38ab https://backend.orbit.dtu.dk/ws/files/9771008/Maria_thesis_final_260612.pdf |
| Summary: | In recent decades, Baltic cod has experienced a period of low recruitment. In the same period the pelagic Baltic Sea ecosystem experienced a regime shift, due to hydrographic changes, affecting all trophic levels. The rationale for the thesis is built on the hypothesis that the regime shift has resulted in decreased dietary value of clupeids in terms of lipid content and essential fatty acids (EFA) which originates from phytoplankton and is transferred up through the food web. Clupeids are main prey for cod in the Central Baltic Sea and a decreased dietary value is hypothesised to affect cod reproduction. The overall objective of the thesis is to investigate the role of lipids in reproduction of cod (Gadus morhua) in the Central Baltic Sea. The first objective is to examine the seasonal variation in content of lipid and EFA in whole prey species of cod (Paper I). The second objective is to investigate the variation in lipid content, EFA and antioxidants of female Baltic cod gonads and livers during the reproductive cycle (Paper II) and to examine whether there is a deficiency in lipid energy and dietary EFA that could explain the delayed spawning time observed in the Baltic cod (Paper III). The third objective is to investigate experimentally if EFA levels, comparable to those observed in Baltic clupeids, delayed timing of spawning and influenced egg production and quality in cod (Paper IV). The study combines field data of cod and its main prey species; sprat (Sprattus sprattus), herring (Clupea harengus) and the isopod Saduria entomon from the Baltic Sea sampled during 2002-2004 and 2008-2009 in different seasons and experimental data of farmed broodstock cod. Lipid composition of whole prey species and ovaries and livers of cod in different maturity stages were analyzed and lipid composition in samples of mature cod was compared with samples of North Sea cod with no delay in spawning time. A feeding experiment was carried out to test the dietary effect of different levels of the essential polyunsaturated n-6 ... |
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