The effects of dietary essential fatty acid enrichment on the nutrition and condition of red king crab (Paralithodes camtschaticus) larvae

Abstract

Alaska red king crab (Paralithodes camtschaticus) is a commercially valuable crab species in Alaska; however, six of the nine red king crab stocks in Alaska are depleted and have failed to recover even after closures of the fisheries. Hatchery rearing is being explored as a possibility for rehabilitating these stocks. In Chapter 1, I review the importance of diet, particularly fatty acids (FAs), when raising crustacean larvae in hatcheries. Long-chain polyunsaturated FAs (PUFAs) are important in molting success, growth, ability to handle stress, and overall survival of crustaceans. Specifically, when the FAs docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3), and arachidonic acid (AA, 20:4n-6) are added to the diet, crustacean survival increases. In Chapter 2 I performed a live-food enrichment experiment in which I tested the importance of dietary ratios of DHA, EPA and AA to red king crab larval growth, survival, and energy storage. Artemia nauplii that were fed to king crab larvae were enriched with four experimental diets, including 1) DHA, 2) DHA & EPA, 3) DHA & AA, and 4) a control diet that had the same total lipid per wet weight but was enriched with oleic acid (OA, 18:1n-9) and had very low PUFAs. Larval condition, assessed by viewing size and number of lipid droplets, was significantly greater at the glaucothoe stage for larvae fed PUFA enriched diets than larvae fed the control OA diet. Larvae that were fed diets enriched with DHA & EPA and DHA & AA had more and larger lipid droplets than larvae that received either the DHA or control (OA) diets. During the high mortality glaucothoe stage the total FAs per wet weight (μg/mg) was significantly lower in crabs fed the control diet. Further, during a salinity stress test glaucothoe previously fed the control OA diet recovered significantly slower than individuals previously fed PUFA-enriched diets, suggesting that PUFAs may improve performance during stress. These results advance our understanding of crustacean larval nutrition and inform the feasibility of rehabilitating king crab stocks that crashed in the early 1980s throughout Alaska.