Date of Award

8-2009

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Linda Kling

Second Committee Member

Nick Brown

Third Committee Member

Denise Skonberg

Abstract

Green sea urchin (Stonglyocentrotus droebachiensis) gonads are sought after in the Japanese market with desirably sized and colored product obtaining high prices. Coupled with the depletion of Maine wild stocks, this makes S. droebachiensis an echiniculture candidate. Current feeding practices usually employ macroalgae to some degree, but feasibility of full life-cycle culture depends on the development of a formulated feed to minimize macroalgae usage while promoting somatic and gonad growth and maintaining gonad quality. Most studies to date have addressed dietary issues using wild-caught S. droebachiensis, but few used hatchery-reared juveniles. Three experiments aimed to elucidate juvenile nutrient requirements and a dietary regime optimizing somatic growth, gonadal-somatic index (GSI), and gonad coloration, while minimizing macroalgae use, in hatchery-reared S. droebachiensis. The first addressed effects of formulated feeds with varying protein and protein-to-carbohydrate levels, a commercial abalone feed, and Saccharina latissima upon somatic growth and GSI. Several prepared feeds (16-37% protein and protein-to-carbohydrate ratios 0.34-1.3) produced equally good somatic growth and GSIs, suggesting variation within these ranges may not be important. Macroalgae produced intermediate somatic growth and the lowest GSI and the abalone feed produced the lowest somatic growth and low GSI despite having values within these ranges, suggesting importance of other nutritional factors. The lowest-protein feed was among the top-performers and was used in subsequent experiments. The second experiment compared effects of this top-performer with two variations of another commercial feed and S. latissima upon somatic growth and GSI. Results suggest that increasing protein, along with gross energy and fat, may promote somatic and gonad growth, as the NoFima 8 diet supported significantly higher somatic and gonad growth and had the highest protein (20.7%), high energy (4.22 kcal/g), and highest fat (5.7%) of any treatment. Amino acid analyses suggest that more glycine, less alanine, and some threshold value of glutamic acid and proline may promote somatic growth, but the best and worst growth-supporting treatments contained protein comprised mainly of glutamic and aspartic acid, suggesting protein type may have been less important than level or absorption. The third experiment compared effects of feeding the top-performer from the first experiment or S. latissima with regimes switching from formulated feed to macroalgae for 4 and 2 months upon somatic growth, gonad yield and coloration. Macroalgae negatively affected somatic and gonad growth, as somatic growth and GSI slowed according to how long macroalgae was fed. Switching individuals from prepared feed to macroalgae at any point did not change gonad coloration, highlighting the importance of dietary history. Gonads from the macroalgae-only treatment were darker, redder, and more yellow than for the prepared feed-only treatment. A tradeoff existed between good gonad coloration and low GSI with macroalgae and high GSI and pale coloration with prepared feeds. GSI and color varied within samples, possibly due to sex. Many factors were uncontrolled including feed formulation, digestibility, protein source ratio, vitamin and mineral content, pigment concentration, temperature, and sex, which, along with other quality parameters, should be addressed in further work with NoFima 8 in market-sized, hatchery-reared S. droebachiensis.

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