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International Waters: Aquarium Water’s Hidden Secrets

Posted: September 26, 2013, 4:00 p.m. EDT

By John Dawes

The saying goes, "Look after the water, and the water will look after your fish,” emphasizing that good-quality water is at the heart of successful aquarium keeping. But does aquarium water hide any secrets, some of which could lead to disease outbreaks among our fish and invertebrates, or even pose a risk to us?

According to a team of four scientists (see end of article for full reference), findings suggest that aquarium tank water harboring ornamental fish is "an understudied source for novel microbial communities and pathogens that pose potential risks to the pet industry, fishes in trade, humans and other species.”

They studied the water in which goldfish (Carassius auratus) and Chinese algae eaters or sucking loaches (Gyrinocheilus aymonieri) bought from seven stores in Rhode Island and New Jersey were bagged following purchase. Two of the stores were part of national chains, while the other five were locally owned small businesses. Specimens of goldfish and algae eaters were kept separate, just as they were in the stores.

Despite appearances, aquarium water harbors an unseen microbial community that warrants further study. John Dawes

In total, 12 goldfish (two from each of six stores) and 14 algae eaters (two from each of seven stores) were purchased.

A sample of 600 milliliters of water from each bag was filtered; the filter cartridges were then air dried, placed in dry ice and stored at below 80 degrees Celsius awaiting analysis. DNA was subsequently extracted from the samples and examined. The results revealed the presence of no fewer than 30 phyla (major lineages) and numerous species of bacteria, some of which pose potential threats to human health, among them Vibrio cholerae, which causes cholera, Legionella pneumophila, which causes Legionnaire’s disease and Pontiac fever, and several species that can cause diarrhea.

In total, the team found 53 genera that contained potentially pathogenic species and 11 species known to cause disease in fish, humans and other species, though they apparently did not detect Mycobacterium marinum, the causative agent of fish tuberculosis, which can be transferred to humans. Other Mycobacterium species were found, however.

The authors of the paper pointed out that the technique used to identify species does not provide the resolution necessary to distinguish between innocuous and virulent organisms, "which can often have identical primary structure along much of the molecule.” That’s why they refer to such organisms as "potentially pathogenic,” recognizing that the transfer of DNA fragments within a species can occur very rapidly, converting an innocuous strain into a virulent one.

They also highlight the fact that many of the potentially pathogenic bacteria they detected in their study "cannot be eradicated, as they are part of the normal microbial flora of myriad hosts and aquatic environments” and that "they are not always harmful.”

Nonetheless, as stated earlier, they believe that their findings suggest that "ornamental fishes and aquarium tank water are an understudied system with highly diverse microbial communities and sources of potential pathogens of interest to the pet industry and public health.” They encourage ornamental fish owners, as well as the ornamental aquatic industry, "to take responsibility for the health of the animals in their care and the people caring for them.”

The researchers suggest that, in the same way as awareness of the risks of salmonellosis has been tackled within the reptile sector, similar programs could be devised for ornamental fish. Further, they express the view that "a multipronged approach that unites consumers, industry and scientists to reduce potential pathogens and disease...seems to be the most realistic way forward.”

Katherine F. Smith, Victor Schmidt, Gail E. Rosen and Linda Amaral-Zettler, Microbial Diversity and Potential Pathogens in Ornamental Fish Aquarium Water. Plos One, Vol. 7, Issue 9, e39971, September 2012.



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