- 學位論文
淡水微藻做為餌料飼養黃金蜆Corbicula fluminea之研究
Evaluation of freshwater microalgal diets for the cultivation of the Asian clam Corbicula fluminea
摘要
黃金蜆（Corbicula fluminea）是一種有價值的臺灣食品、成分及營養補充品。蜆的生物量需要透過適當培養來增加，而微藻是軟體動物成長中重要的食物來源。本研究自彰化縣的黃金蜆養殖場中分離出五種淡水微藻，分別為 Chlorella pyrenoidosa、Pilidiocystis multispora、Tetradesmus obliquus、Coelastrum microporum 及Cyclotella cryptica。在初步的研究中，分別以五種微藻作為餌料飼養黃金蜆， 評估微藻對於蜆的生長和存活率之影響。 結果顯示， 檢測黃金蜆蜆肉乾重以 C. pyrenoidosa 培養可以得到最佳蛋白質含量 58.34%，而以 C. cryptica 培養黃金蜆蜆肉乾重中有最高脂質含量 25.06%。相關分析說明，蜆肉中的蛋白質和脂質含量與微藻中的蛋白質和脂質含量呈正相關。以 C. pyrenoidosa、P. multispora 及C. cryptica 培養黃金蜆時，蜆殼殼長增加率、活體增重率和存活率各相對應呈最大百分比。然而， 以 T. obliquus及C. microporum 餵養蜆時，因餌料大小不適當致使黃金蜆增重速度為負成長。因此，選擇C. pyrenoidosa 、 P. multispora 及 C. cryptica 等藻種培養黃金蜆，可促進蜆的生長及其營養價值。 為了使微藻作為更有價值的生物資源， 必須確定生長條件對藻類產量和生化產量的影響。以 Box-Behnken 對環境條件進行優化，提高三種選定微藻餌料的產量， 分別針對三種微藻其溫度、 光照及pH值進行優化，C. pyrenoidosa 培養的條件是 25 ℃、180 μmol photons m-2 s-1及 pH 8.48。在 25.70 ℃、173 μmol photons m-2 s-1及pH 8.35 的情況下，適用於 P. multispora 的培養。 最後是以 26.56 ℃、182 μmol photons m-2 s-1及 pH 7.63 的條件，適合 C. cryptica 的培養。在這些優化條件下，微藻生物量、脂質及蛋白質含量均顯著增加。 優化微藻後，進行為期 8 週培養試驗，以確定單一或混合微藻餌料對黃金蜆生長的影響。 研究結果顯示， 在所有組別中均觀察到高存活率。 比較單一及混合培養， 微藻混養對黃金蜆的生長具有更好的效果，因為營養素補充混合物滿足蜆的營養需求。蛋白質是蜆肉的主要成分，黃金蜆蜆肉的總蛋白質含量範圍為乾重的 55.90 - 62.55%。當以 C. pyrenoidosa 與 C. cryptica 混合（餌料1 + 3）培養黃金蜆時，發現蜆的殼長、增重及乾肉重量增長最快。在餌料 1 + 3 中發現較高的蛋白質含量 （占乾重的 37.84%）、 脂質（占乾重的 28.79%）及總 PUFA 占 45.69%。在餌料 1 + 3 中 蜆的生長速度與高蛋白、脂質、ALA 及總 PUFA 含量呈正相關，適合蜆的生長。 此外，以 1 + 3 混合餌料培養的蜆在蜆肉中的蛋白質含量方面表現出出色的結果 （占乾重的 61.08%）。 黃金蜆蜆肉中富含的脂肪酸為 C16：0 、 C16：1 、 C18：3 、總 PUFA（42.84%）和總 omega-3（33.15%）。 在黃金蜆養殖的環境水質監測，以溫度、pH 值、溶氧及總鹼度符合最佳範圍內，對於蜆類生存是安全的。每天以 50% 的比例更換容器中的水，以避免 NH3-N 或NO2-N 濃度的累積，同時可以降低蜆的死亡率。
並列摘要
The Asiatic clam, Corbicula fluminea, is a valuable Taiwanese food, ingredient, and nutritional supplement. It is necessary to increase the biomass of the clam by culturing it with a proper diet. Live microalgae are an essential food source for the mollusk growth. Five useful freshwater microalgae, C. pyrenoidosa, P. multispora, T. obliquus, C. microporum, and C. cryptica were isolated from a clam culture farm in Changhua, Taiwan. The potential of food availability on C. fluminea clam growth and survival was studied by rearing the clam with five microalgal diets as a preliminary study. The greatest protein content found in the clam meat was when it was fed C. pyrenoidosa (58.34% dry weight). C. cryptica stimulated the highest lipid content in the clam meat (25.06% dry weight). The correlation analysis illustrated that the protein and lipid content in the clam meat were associated positively with protein and lipid content in the microalgal diet. The maximum percentage of clam growth rate on shell length, live weight gain, and survival rate was found when fed C. pyrenoidosa, P. multispora, and C. cryptica, respectively. However, the clams experienced a negative growth rate in terms of weight gain when fed T. obliquus and C. microporum due to an inappropriately sized of diet. Therefore, C. pyrenoidosa, P. multispora, and C. cryptica were selected to support clam growth and nutritional value. To utilize microalgae as a valuable bioresource, the effect of growth conditions on algal yield and biochemical production must be determined. The environmental conditions were optimized to accumulate higher production of three selected microalgal diets by Box-Behnken design. As per the model conditions, the optimized condition was performed at 25°C, 180 μmol photons m-2 s-1, and pH 8.48 for stimulated C. pyrenoidosa production. At 25.70°C, 173 μmol photons m-2 s-1, and pH 8.35 it was suitable for P. multispora production. Lastly, the conditions 26.56°C, 182 μmol photons m-2 s-1, and pH 7.63 were better for the production of C. cryptica. Under these optimized conditions, the biomass, lipid, and protein content increased significantly. After optimizing the microalgae, a feeding trial was conducted to determine the effect of single and mixed microalgal diets for the growth of C. fluminea clam for eight weeks. A high survival rates were observed in all the dietary groups. Feed mixtures had better results on clam growth compared to single diets, as mixtures contain a complementary blend of nutrients that meet the nutritional requirements of the clams. Protein was a major constituent in all the clam meats. The overall protein content of clam meat ranged significantly from 55.90-62.55% of dry weight. The highest growth of shell length and weight gain and dry meat weight of the clams was found when fed on the mixed diet of (diet 1+3) C. pyrenoidosa mixed with C. cryptica. The comparatively high amounts of protein (37.84% of dry weight), lipid (28.79% of dry weight), and total PUFAs at 45.69% were found in diet 1+3. The growth rate of the clams associated positively with high content of protein, lipid, ALA, and total PUFAs, obtained in the diet 1+3 which is appropriate for the growth of the clams. Moreover, the clams fed on the mixed diet of 1+3 demonstrated outstanding results for protein content (61.08% of dry weight) in the meat. The abundant fatty acids were C16:0, C16:1, C18:3, total PUFAs (42.84%), and total omega-3 (33.15%) were found in the clam meat. For environmental water quilaty monitoring in the clam experimental container, water temperature, pH, dissolved oxygen, and total alkalinity were in the optimum guideline ranges for the protection of aquaculture species and were safe for clam survival. It is necessary to change and replace water in the container on the basis of 50% per day to avoid the accumulation of NH3-N or/ NO2-N concentrations and reduce the clam mortality rate.