The Effects of Dietary Lipids and Fatty Acids on Juvenile Tanner Crab (Chionoecetes bairdi) Growth Rates

Tanner crabs compose a locally important fishery in the northeast Pacific and Bering Sea, however little is known regarding their optimal growing conditions. In recent years, juvenile crabs of drastically different sizes were recovered from several bays in Kodiac Island, Alaska. This study will determine what portion of the observed variation in growth can be attributed to differences in diet between the bays, having implications for crustacean hatchery strategies as well as for wild population management. In the laboratory, we will rear C1 tanner crabs on seven different dietary treatments, varying total lipid content and levels of two different essential fatty acids to mimic prey quality variation in the wild. The two poly-unsaturated fatty acids (PUFA) we are particularly interested in are docosahexaenoic acid (DHA, 22:6ω-3, correlated with dinoflagellates) and eicosapentanoic acid (EPA, 20:5ω-3, correlated with diatoms). We will test the hypothesis that total lipid levels will result in higher growth rates, total long chain PUFA will result in higher growth rates, and higher ratios of EPA relative to DHA will result in higher growth rates. Growth rates will be determined by recording intermolt period, as well as molt increment. Lipid extraction and analysis of stage C3 crabs, in conjunction with fatty acid analysis, will demonstrate how crabs are utilizing dietary lipids.  Results from this study will further knowledge concerning optimal diet composition, and will fill a knowledge gap in our understanding of lipid and fatty acid use in the Pacific Ocean.