Are the leaves and stems from ornamental sweet potato vines poisonous to koi? I've done searches here and on other websites and get conflicting reports. I have vines and leaves hanging down into the lower pond along side the waterfall and the fish sure seem to be enjoy chowing on them...looks like they're trying to pull the plant into the water. This has been going on for a few days, so I'm leaning towards it not hurting them, but wondered if it was something that could build up in their system....thanks