飼料中添加有效的微生物對日本鰻Anguilla japonica玻璃鰻生長發育、腸道形態、免疫和抗病性的影響

Abstract

日本鰻 (Anguilla japonica) 是臺灣、日本、中國和韓國的重要經濟養殖魚類。台灣的鰻魚養殖業曾是全球的重要供應者。由於鰻苗資源的減少、環境變遷以及疾病等因素，近年來鰻魚養殖面臨着諸多挑戰。台灣的養殖業者引進集約化循環水系統來提高養殖效率和產品品質。隨著鰻魚養殖日益集約化，細菌性疾病逐漸成為鰻魚養殖主要威脅，愛德華氏菌（Edwardsiella tarda）感染是魚類養殖中常見的細菌性疾病之一。養殖者通常添加抗生素來抑制疾病的發生，但長期使用抗生素會出現抗藥性問題，因此，養殖者期望添加功能性生物飼料添加劑或益生菌來實現環境友善，增強魚類的免疫力和提高生長性能。「 EM 」（Effective Microorganisms） 是一種由乳酸菌、酵母菌、光合成細菌等多種有益微生物組成的菌種，在水產養殖業中應用時有助於水質管理、動物健康、污染減少等，提升養殖效益並降低生態影響。本實驗探討在飼料中添加不同比例的EM菌對於日本鰻玻璃鰻生長發育、腸道形態、免疫和抗病性的影響。實驗採用200尾日本鰻，分為 5 組，每組進行 2 重複。這5組分別被餵養添加了不同濃度EM菌的飼料，分別為0%（對照組）、0.5%、1%、2%和5%。各組添加的EM菌經過精密天平稱量，加入各組基礎的膏狀飼料中混合攪拌混勻。每 14 天測量鰻苗的長度與體重，每日記録死亡數量和餵食情況，分析其生長性能。本實驗實驗周期為12週，實驗結束後每缸犧牲 4 尾，採集腸道、頭腎。採集的腸道進行石蠟包埋，切片觀察腸道形態及腸道絨毛狀態。採集的頭腎進行 qPCR 分析免疫相關基因表現。愛德華氏菌用於攻毒試驗。本研究顯示，在鰻魚飼料中添加2%有效微生物為最適劑量，能顯著提升腸道中益生菌如 Bacteroides、Faecalibacterium 與 Alistipes 的相對豐度，並抑制如 Prevotella 等潛在致病菌，促進腸道菌相的多樣性與穩定性，進而增進腸道健康與整體生理機能。相較之下，雖然5%添加組亦能改變菌相組成，但易造成菌群結構過度偏向特定菌屬如 Megasphaera，降低整體多樣性，需審慎評估其長期影響；而0.5%以下劑量則效果有限，與對照組差異不明顯。在生長表現方面，2% EM添加組在12週試驗期間呈現最佳的體重與體長增長，顯著優於其他組別，顯示其有助於提升鰻苗的飼料利用率與營養吸收效率。此現象可能與腸道健康改善、腸道絨毛結構優化及微生物群落平衡有關，從而促進養殖成長效率。免疫基因表現分析亦指出，2% EM組可顯著促進頭腎中與免疫、發炎及抗氧化相關基因的表達，包含提升非特異性免疫酵素活性（如 lysozyme）、調節發炎因子（如 TNF-α）、並減輕氧化壓力。綜合七項指標基因的表現結果，2%添加組展現出穩定且全面的免疫調節效果。此外，攻毒實驗結果亦顯示，2% EM組具有最高的生存率與最強的抗病力，證實適量的複合益生菌可有效強化鰻苗之抗病能力與存活表現。整體而言，2% EM添加量為本試驗中各項生理指標表現最佳之劑量，不僅具調節腸道菌相、促進免疫功能與提升抗病力之潛力，亦能有效促進生長表現。建議實際應用中採用2% EM菌添加量，並進一步追蹤其於不同生長階段與養殖條件下之長期效果，以優化鰻魚健康養殖策略與經濟效益。

Japanese eel （Anguilla japonica）is an economically important aquaculture species in Taiwan, Japan, China, and South Korea. Taiwan was once a major global supplier of farmed eels. However, in recent years, eel aquaculture has faced numerous challenges due to the depletion of eel fry resources, environmental changes, and disease outbreaks. To improve production efficiency and product quality, Taiwanese aquaculture farmers have adopted intensive recirculating aquaculture systems (RAS). With the increasing intensification of eel farming, bacterial diseases have become a major threat, among which Edwardsiella tarda infections are one of the most common bacterial diseases in aquaculture. Although antibiotics are commonly used to control disease outbreaks, long-term use can lead to antibiotic resistance. Therefore, farmers are seeking environmentally friendly alternatives, such as functional feed additives and probiotics, to enhance fish immunity and growth performance. Effective Microorganisms (EM), a mixed microbial culture composed of lactic acid bacteria, yeasts, photosynthetic bacteria, and other beneficial microbes, have been widely used in aquaculture for water quality management, improving animal health, reducing pollution, and enhancing overall farming efficiency with minimal ecological impact. This study investigated the effects of different dietary EM supplementation levels on the growth, intestinal morphology, immune responses, and disease resistance of Japanese glass eels (Anguilla japonica). A total of 200 eels were divided into five groups with two replicates per group. The groups were fed diets containing 0% (control), 0.5% , 1% , 2% , and 5% EM. All EM concentrations were accurately weighed and evenly mixed into the basal paste feed for each group. Body length and weight were measured every 14 days, and daily records of mortality and feeding behavior were maintained to evaluate growth performance. The feeding trial lasted for 12 weeks. At the end of the experiment, four eels from each tank were sacrificed to collect intestinal and head kidney samples. Intestinal samples were processed using paraffin embedding and histological sectioning to observe intestinal morphology and villus structure. Head kidney samples were analyzed by qPCR to assess the expression of immune-related genes. E.tarda was used for pathogen challenge tests. The results indicated that EM supplementation generally improved the growth performance compared to the control group. The group fed with 2% EM showed the longest intestinal villi, suggesting the best digestive and absorptive efficiency. Furthermore, EM supplementation enhanced immune activity, reduced intracellular stress and inflammatory responses, suppressed potential pathogenic bacteria, and increased survival rates following E. tarda challenge. Based on these findings, a 2% EM supplementation level is recommended for practical application, with long-term monitoring to further optimize eel farming efficiency and health management strategies.