The symptoms of black tongue in cats may be caused by oral ulcers, Toxoplasma gondii, hypoxia and other reasons. Long-term feeding of nutritional paste to cats can also cause black tongue in cats. When this happens, you can take the cat to the pet hospital for examination and treatment to avoid delaying the condition. Cats should be regularly vaccinated and dewormed, and fed some light and easy-to-digest food to promote their healthy growth.