Goldfish and Aquarium Board Articles
Medicated Food Explained and Explored
By Liv

The Advantages of Medicated Food
The Disadvantages of Medicated Food
Anti-Parasitic Food
Anti-Bacterial Food

A few years ago when Tetra stopped producing anti-parasitic fish food, the company explained that there was not enough demand for the product. But thankfully aquarium keepers have again started to look into this option for their sick fish and we now have several important options available to us hobbyists for when we have to treat our sick fish. This article outlines the available common medications, discusses the ingredients and attempts to narrow down which medicated drug may be better for our needs.

The advantages of medicated food
Medicated food provides a greater chance that the active ingredients will be absorbed by the sick fish, something that is important if what we want to treat is internal rather than external. The other option available to most fishkeepers is often water borne medications. Water borne medications will have to be either absorbed through the gills or the skin of the fish (as fish do not exactly drink water). And for some of the medications we may want to use, it is unclear what the absorption rate of the medication is. A final option is injections and while injections are a superior method they may not be practical or possible for many hobbyists.

The disadvantages of medicated food
In some cases if the fish gets ill it will not want to eat and medicated food will be useless. Sometimes it is hard to know how much food we need to feed in order to ensure that the 'patient' is getting enough medication


There are several types of internal parasites. They are hard to diagnose as necroscopy (examine fish, intestines in particular under a microscope after death) is often the only accurate way. Sometimes failure to thrive and losing weight (even if the fish is eating) are indications of an internal parasitic infection. Camillanus is an exception, as the worm protrudes from the anus of the fish which makes identification easier.

Common Internal Parasites

Common Anti-parasitic medicial foods on the market

In conclusion
The choices (in North America) for medication addressing internal parasties seem to be good. Jungle or Ultra Cure PX make good choices with medical ingredients that cover most common parasites.


There are a wide range of bacterial infections that may affect our fish such as finrot, septicemia, flex and ulcers. Many of these infections will have external signs but originate internally and can be addressed by feeding food containing antibiotics. Bacterial illness may be caused by many different kind of bacteria, the most common being Aeromonas hydrophila, Aeromonas salmonicida, Flavobacterium columnare (which causes columnaris), Vibrio, and Pseudomonas species. Bacteria are usually classified as either gram positive or gram negative depending how they react to the gram staining test. Most bacteria we will deal with are gram negative and thought to be better treated with anti-bacterial meds that are protein inhibitors. Most of the medical ingredients in the bacterial food referred to contain protein inhibitors (Kanacyn and Oxolinic Acid are exceptions).

Sometimes it makes sense to combine a water antibiotic with a medicated food. However, some antibiotics should not be used together, so the antibiotics you choose have to be compatable or they may not work properly.

Anti-bacterial medication is normally either bacteriostatic or bactericidal. Bacteriostatic means that the medication aims to inhibit growth of the bacteria but allow the immune system to actually kill the bacteria. Bactericidal means that the medication aims to kill the bacteria. When we use medication that is bactericidal it *may* have a negative impact on the nitrifying bacteria in our biological filter.

Common Anti-Bacterial Products on the North-American Market

Conclusions: For antibacterial food Medi-Gold is a very good option as its combination of antibiotics addresses a wide range of bacteria. There are also reports of bacterial resistance to sulfa drugs-a key ingredient in many of the other medications discussed here. Because of this, some people add another anitbiotic Trimethoprim to help strengthen the sulfa drugs. The combination forms are called a potentiated sulfa. Trimethoprim can only be obtained from a vet.

Things to remember.
Medical ingredients have short shelf lives. Pay attention to the date on the product. After opening, store the product according to instructions. Remember to feed only medicated food while you are treating and to feed for the whole period recommended.

May your fish live long and prosper.


Edward Noga, Fish Disease: Diagnosis and Treatment

Klinger and Floyd: Introduction to Freshwater Fish Parasites (pdf)

Beverly Dixon, Antibiotics: How Do They Work Aquarium Fish Magazine Febr. 1992

Dieter Untergasser, Handbook of Fish Diseases

Roy P. E. Yanong: Use of Antibiotics in Ornamental Fish Aquaculture.

Ruth Francis-Floyd and Peggy Reed: Use of Medicated Feed in Channel Catfish.

The Merck Veterinary Manual online.

Printable version of this article