Effects of water temperature, age of feces, light intensity and shelter on the consumption of sea urchin feces by the sea cucumber Apostichopus japonicus

The Integrated Multi-Trophic Aquaculture (IMTA) of sea cucumbers and sea urchins has high commercial values. The consumption of sea urchin feces by sea cucumbers is important but largely unknown. The present study aims to evaluate and subsequently improve the fecal consumption in sea cucumbers. Sea cucumbers ingested the feces of sea urchins at both 15 degrees C and 5 degrees C, suggesting that the feces of sea urchins has potential to be an appropriate diet for the aquaculture of A. japonicus. Because feces has a complex process after the egestion, the age and temperature significantly affected the fecal consumption by sea cucumbers. The optimal ageing time after egestion was 0-48 h at 15 degrees C, 0-72 h at 5 degrees C, respectively. Thus, we recommend aqua-farmers feed A. japonicus with feces at the optimal ageing hours and remove the feces in time. Further, light intensity significantly affected the fecal consumption by A. japonicus. Sea cucumbers had significantly more fecal consumption in low light intensity than that in high light intensity at both 5 and 15 degrees C. Further, sea cucumbers fed significantly more in low light intensity with shelters than those in low light intensity without shelter, suggesting that shelter provides extra benefits for the fecal consumption by sea cucumbers besides the low light intensity. In addition, significant feeding benefits were found in both low light intensity and shelter at low temperatures. This may solve the problem that sea cucumbers cease feeding at 5 degrees C in winter. Organizing IMTA in sheltered environment and low light intensity can improve fecal consumption at both 15 degrees C and 5 degrees C. The present study provides valuable information in evaluating and improving consumption of sea urchin feces by A. japonicus in the IMTA of sea cucumbers and sea urchins.