No.

According to Baidu’s experience data, Alisma is a common aquatic plant. It has no obvious toxicity to fish and usually does not cause direct harm to the health of fish. However, when Alisma grows too much in a fish tank, it will consume nutrients and oxygen in the water, resulting in poor water quality and thus affecting the health of the fish.

Alismatis is the dried tuber of the Alisma family plant. Alisma tastes sweet and light, and is a cold-nature medicine. Returns to the kidney and bladder meridians.