Novel findings in sea cucumber's digestive capacities: Enzymatic activities in the respiratory tree, implications for aquaculture

Abstract

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 membranelinked 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

Influence of Dietary Phosphorus on the Growth, Feed Utilization, Proximate Composition, Intestinal Enzymes, and Oxidation Resistance of Sea Cucumber Apostichopus japonicus

“…On the other hand, the estimated dietary phosphorus requirement from these quadratic regression analyses appears lower than the published reports on fish (0.72-1.57%, [28,[51][52][53]), shrimp (1-2%, [26,[54][55][56][57]), crab (1.59-1.68%, [24]), and abalone (1-1.2%, [25]), implicating that sea cucumber may have an specific phosphorus acquisition mechanism. This is proved by a recent physiological findings indicated the phosphatase exhibited comparable activity levels in the respiratory tree segments of sea cucumber Isostichopus badionotus [58]. Another evidence from an early P 32 isotope study also revealed that sea cucumber absorbed a limited amount of phosphorus from the environment through the integumentary surface and respiratory tree [59].…”