TAKEMAE, N.; NAKAYA, F.; MOTOKAWA, T.; Tokyo Institute of Technology; Tokyo Institute of Technology; Tokyo Institute of Technology: Oxygen consumption of catch connective tissue of the sea cucumber Actinopyga mauritiana (Echinodermata, Holothuroidea)

Sea cucumbers show lower oxygen consumption rate per wet weight (VO₂) compared to other animals of the same size. This has been attributed to the high content of connective tissues. Sea cucumbers have a thick body wall composed mainly of the connective tissue dermis whose VO₂ is supposed to be low. Another reason has been attributed also to connective tissues. Echinoderms have catch connective tissues (CCTs) that change their mechanical properties. Sea cucumbers use CCT in body walls, instead of muscles, in posture maintenance. The posture maintenance by CCT has been speculated to use less energy. There are, however, no detailed reports on what extent connective tissues occupy the holothurian body and there are no measurements on VO₂ of connective tissues. We estimate the volume of connective tissue and muscle by dissection and histological sections. The connective tissue occupied more than 50 % of the body weight; muscles occupied only 5.4 %. We measured VO₂ of the connective tissue dermis both in catch (stiff) state and out-of-catch (relaxed) state by oxygen electrodes. VO₂ of the longitudinal body wall muscles was also measured in contracted state and relaxed state. VO₂ of the relaxed connective tissue was about 1/6 of the relaxed muscles. The oxygen consumption increased by 1.4 times when CCT became stiff. The increased value of the stiff CCT was, however, only 1/10 of VO₂ of the contracted muscles. These results provided the evidence that the posture maintenance by CCT is more economical than by muscles. The present work showed that both the exceedingly high content of connective tissues and the use of CCT for posture maintenance contributed to the low energy expenditure of sea cucumbers.