Not overly conclusive by any means, but interesting nonetheless. Both Dr. Edward J. Noga and the North Carolina State University, College of Veterinary Medicine are well known for their work with fish. Noga's book on fish health/illness is pretty much the bible for anyone who is seriously interested in this field, including vets who specialize in fish.
Laboratory Evaluation of Safety and Efficacy for Melafix (Melaleuca cajuputi Extract)
http://www.exoticpetmedicine.com/article/S1557-5063(15)00026-9/abstract
Laboratory Evaluation of Safety and Efficacy for Melafix (Melaleuca cajuputi Extract)
http://www.exoticpetmedicine.com/article/S1557-5063(15)00026-9/abstract