Common Parasites

If you have ever kept fish you have probably heard of Ich. Ich is a small tick like parasite that looks like a salt granule. This common parasite is always present in aquariums. When fish are under stress it is possible for them to “catch” Ich. This is similar to when you are stressed, your immune system is weakened and you may catch a cold.

So why is the fish stressed?

Temperature flux – a daily change of temperature of 3 degrees or more will cause problems for many fish especially marine fish. Check your temperature first thing in the morning and again just before turning out the lights and compare the difference. Set an aquarium heater at the higher temperature if necessary.

Inappropriate pH – Salt water fish need to be maintained at 8.2-8.3. Most fresh water fish are happy with a neutral pH of 7.0, however, Discus and rummy nose tetras prefer soft acidic water with a pH around 6.0. African cichlids like hard water with a high pH 7.8-8.2. Gold fish and live bearers such as sword tails, platys, guppies, and mollies do well in a pH around 7.5.

High waste levels – Any ammonia or nitrite will cause stress on fish, it can literally burn them. Also high nitrates sustained over time will wear fish down and weakens there immune system.

Psychological stress – even subtle domination among tank mates is enough to cause too much stress. Your fish can see you as well as you see them, therefore, there behavior changes when you enter the room making it difficult to catch a bully in the act.

Passive slower moving fish will suffer being housed with fast voracious fish even if they are not directly picked on.

So before you dump medicine in you aquarium try to figure out why your little friend got Ich in the first place and correct that problem first, and then if necessary medicate.

A natural way to inhibit Ich’s reproduction in marine aquariums is to lower the salinity – -density. Adding aquarium salt to a fresh water tank will have the same benefits.

Some fish are more susceptible to Ich than others, for example many Tangs seem to have less resistance to Ich than other fish.


Oodidium (or Marine Velvet) is a parasite that begins in the fish’s gills and then spreads over the body. This parasite is not visible to the naked eye until it is pretty well advanced so early detection is crucial. The first sign is rapid or labored breathing; as it advances symptoms include flicking of the fins and scratching on the bottom and against rocks. Finally the fish appears cloudy especially on the eyes and fins. There are so many parasites on the gills by now that the fish may be gasping at the surface or swimming into the current trying to get more oxygen. Before the fish’s death the parasites have grown enough to be barely visible tiny white spots, the fish looks pale and velvety over the entire body hence the name Marine Velvet.

This parasite is so dangerous because each parasite lays hundreds of eggs, therefore major infestation can occur in no time. Some people lose all there fish relatively quickly but to further complicate things some fish are naturally resistant to this parasite and do not succumb to it. This can make diagnosis difficult for the novice.

The resistant fish looks and behaves normal but each time a new fish is introduced to the tank it may die surprisingly fast, even within a day or two.
Treatment: First the aquarium must be a stable (temperature & pH) and healthy environment (waste levels in check). Fish should be fed well to keep up there strength, a garlic supplement may be added to food to enhance appetite and potentially inhibit parasites. Copper is the most effective medication and generally shows surprisingly quick results (I recommend Cupramine, it seems to be easier to remove after treatment than some other brands). Unfortunately if you have invertebrates like corals, anemones, starfish, shrimp, etc. copper is not an option. If infection is diagnosed very early “reef safe” medication may be effective. When treatment is not an option the only thing to do is starve the parasites out by not adding new fish for a minimum of one to two months. In an effort to avoid this whole problem observe the fish at the store several minutes for symptoms before buying it and find a knowledgeable trust worthy fish expert to guide you.


Flukes are a widely unrecognized problem. If you notice your fish slowly loosing weight and occasionally scratching against objects it may have flukes. Flukes are a small virtually invisible leech like parasite that is 1/8” or smaller. If a fish is infected and a fluke attaches to the lens of its eye the eye will become irritated and become cloudy. Flukes are not uncommon, especially in the summer, but the good news is once identified they are easy to treat with a reef safe medication called praziquantil. If you notice the above described behavior just medicate, it can’t hurt.