Parasites, water changes and bottom cleaning

Q. Your latest articles are related to fish diseases.
As you writes in Parasite Surveys of Aquarium Fish: «[…] an unexplained illness in my guppies prompted me to start digging into the scientific literature».
Was this the only reason? Or do you think that on fish diseases common explanations and information are often misleading?

A. Not misleading, just not useful. If you look at any diagnostic chart, fish disease textbook, internet website, etc, you’ll see a bewildering list of fish diseases. Not very helpful. My article, drawing on 11 health surveys, shows what are the most common pathogens carried by fish being sold to hobbyists. In researching the article, I was stunned to learn that it was not bacteria, not mycobacteria, not viruses but parasites, especially Monogenean flukes. If hobbyists know what pathogens cause the most problems in the aquarium industry, it simplifies the diagnosis and treatment. For example, they don’t need to waste time and money treating miscellaneous, unidentified diseases with antibiotics against bacteria when the evidence shows that the most common pathogens are—by far—parasites.

Frequent water changes, bad general conditions and stress cause frequently the appearance of parasites in domestic aquariums; which are the best ways to avoid them or at least to reduce the problem? Do you think to write other articles on this topic?

In my experience, newly purchased fish are always the ones that cause problems, both for themselves and their tankmates.  Stress reduction will reduce many diseases, but not always.  For example, if newly purchased fish are infested with the nematodes Camallanus or Capillaria, stress reduction won’t make the problem go away.  Sooner or later, these intestinal parasites will cause disease.

After starting up with guppies last year, it took me several months to clean them up. I had to eradicate two different parasites: Camallanus worms and later the Gyrodactylus flukes. Now, the fish are thriving.  I’ve got female guppies producing babies at 9 weeks!

I do not plan to write another article on fish diseases. My next one will probably be on raising and breeding guppies. But I need more time and experience with the genetic stuff, which has turned out to be incredibly complicated.

Q. Has your opinion changed over the years about water changes or do you continue to consider them unnecessary and to be done only if problems occur?

A. No. My opinion about water changes has not changed.

However, I would advocate removing debris from the tank bottom, especially in quarantine tanks or tanks with new fish (so many parasites lay eggs that sink to the bottom).  Similarly, I would argue for removing oily biofilms from the water surface, since this is where mycobacteria, the cause of «Fish TB», tend to congregate.

Q. Bottom cleaning could be necessary in quarantine tanks, but do you think it’s necessary in a natural tank setup which has been established for a long period of time?

A. No. Once a natural tank is well-established after about 3 months and doing well, cleaning can be detrimental.  It removes plant nutrients.