Fish mox is one of the many fish antibiotics that are used to treat bacterial infections in ornamental and pet fish. The antibiotics that are used to treat them are the same or similar to the antibiotics that are provided for human use, as well. Fish antibiotics currently on the market are available without a prescription and mainly come in lots of approximately 30-100. Labs make several forms of them, including capsules, tablets, single- use powder packets and pure bulk powder jars.