A POSSIBLE ROLE OF THE RESPIRATORY TREE OF Isostichopus badionotus SEA CUCUMBER AS AN ACCESSORY ORGAN TO DIGESTION, AND ITS IMPLICATIONS IN AQUACULTURE

The sea cucumber Isostichopus badionotus Selenka is a detritivorous species distributed in the tropical western Atlantic including the Gulf of Mexico, the Caribbean Sea and the Gulf of Guinea in Africa.  Its populations are under overexploitation, which has stimulated efforts for its culture. Among the main challenges for its rearing in captivity is the development of adequate diets and feeding protocols for the different phases of its culture, for which, the knowledge of its digestive physiology is essential. In this study were evaluated some of the main digestive capacities of wild adults of  I. badionotus  caught off the coast of the port of Progreso , Yucatan, Mexico. The organisms were dissected immediately after capture to extract the digestive tract (DT) and the respiratory tree (RT), the latter considering previous reports of assimilation of nutrients. DT was divided into three regions: Foregut (FG), including pharynx, esophagus, and stomach; Midgut (MG) and Hindgut (HD). RT was analyzed as a whole.  The samples were frozen immediately in liquid nitrogen, lyophilized and homogenized to obtain extracts for analysis of the enzymes leucine-alanine peptidase (LAP), aminopeptidase (APN), acid phosphatase (AcP), bile salt-activated lipase (BAL), laminarinase (LAM) and β-glycosidase (BGL), using standardized methods for each one.

The activity of the studied enzymes was detected in all the tissues analyzed, and except for BGL and LAM, the levels were statistically similar among tissues, including the respiratory tree. The activity of BGL was significantly higher in MG and lowest in RT; since LAM activity was higher in the FG compared with RT (Figure 1). These results suggest a preponderant role of RT in the sea cucumber digestion, possibly as an adaptive response to the oligotrophic environment where they live. This result leads to the development of feeding protocols that consider the use of phytoplankton, microparticle-diets, or nutrients dissolved in the water column, especially in the hatcheries, where high mortality occurs in early juveniles during the transition from planktonic to benthic feeding and through the growing stage.