There is a demand for proper feed and feeding strategies in the growing sea cucumber aquaculture. The digestive system of holothurians seems to increase nutrient assimilation through the respiratory tree (RT), but digestive functioning in this organ has not been investigated. This study evaluated the enzymatic activity of the cytosolic leucine alanine peptidase (leu-ala) and acid phosphatase, the membrane-linked aminopeptidase-N (APN), the bile salt-activated lipase, laminarinase (LAM), and β-glycosidase (BGL), in the RT and segments of the digestive tract (DT; foregut, midgut, and hindgut) of adult Isostichopus badionotus. All enzymes, except LAM and BGL, exhibited comparable activity levels in the RT and the DT segments, but APN and BGL activities were significantly higher in the whole DT compared with those in RT, with high activity of leu-ala in both organs. These results indicate a relevant role of the RT as an accessory organ in sea cucumber digestive physiology. Consequently, I. badionotus seems to be able to digest feeds from the water column through the RT, maximizing the use of available nutrients by luminal, intracellular, and apical membrane-linked digestive modes. These findings expand the knowledge of sea cucumber digestive mechanisms, with implications for developing feeding strategies for all life stages in aquaculture.

中文翻译：

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海参消化能力的新发现：呼吸树中的酶活性，对水产养殖的影响

在不断增长的海参水产养殖中，需要适当的饲料和饲养策略。海参的消化系统似乎通过呼吸树 (RT) 增加营养吸收，但尚未研究该器官的消化功能。本研究评估了细胞溶质亮氨酸丙氨酸肽酶 (leu-ala) 和酸性磷酸酶、膜连接氨肽酶-N (APN)、胆汁盐活化脂肪酶、海带多糖酶 (LAM) 和 β-糖苷酶 (BGL) 的酶活性。 )，在成年Isostichopus badionotus的 RT 和消化道段（DT；前肠、中肠和后肠）. 除 LAM 和 BGL 外，所有酶在 RT 和 DT 片段中都表现出相当的活性水平，但与 RT 中的相比，整个 DT 中的 APN 和 BGL 活性显着更高，两个器官中 leu-ala 的活性都很高。这些结果表明 RT 作为辅助器官在海参消化生理学中的相关作用。因此，我。badionotus似乎能够通过 RT 消化来自水体的饲料，通过腔内、细胞内和顶膜连接的消化模式最大限度地利用可用的营养物质。这些发现扩展了海参消化机制的知识，对制定水产养殖各个生命阶段的饲养策略具有重要意义。