I'm not positive but I think it's water because more substances dissolve in water than any other substance so, you can at least try it!!!
We can rule out small fish and grasses. My guess is that zooplankton get their energy from phytoplankton, because phytoplankton use photosynthesis to get their energy.
Ileocecal sphincter tone decreases after distention of colon. This sphincter separates ileum and cecum and is under the control of vagus nerve.
