The findings raise concern that treatments for fish diseases may not work when needed and also lead to worry of creating yet another mechanism for exposing humans to antibiotic-resistant bacteria, they said.
Although the risk to humans is probably minor unless they frequently work with fish or have compromised immune systems, transmission of disease from tropical fish has been documented and there are few regulations in the United States or elsewhere concerning treatment of ornamental fish with antibiotics, experts said.
Antibiotics are used routinely when tropical fish are transported whether or not they have shown any sign of disease, they said.
In a study, 32 freshwater fish of various species were tested in Portland, Ore., after being transported from Colombia, Singapore and Florida, for resistance to nine antibiotics, with some resistance found to each, researchers said.
"We expected to find some antibiotic resistance, but it was surprising to find such high levels, including resistance in some cases where the antibiotic is rarely used," said Tim Miller-Morgan, a veterinary aquatics specialist with Oregon State University. "We appear to already have set ourselves up for some pretty serious problems within the industry."
The ornamental fish industry involved trade of more than 6,000 species of freshwater and marine fish from more than 100 countries, with about half the supply coming from Asia.