the Goldfish ich Cycle

The disease known as “ich” is short for ichthyophthiriasis; it is caused by the formation of a parasite called ichthyophthirius multifiliis. This is a single celled organism (or protozoan), it can move, and feeds on organic compounds of nitrogen and carbon ((e.g. an amoeba). In fact, ich is so successful it has become one of the most common of captive goldfish diseases, and is sometimes responsible for more goldfish deaths than any other disease. The parasite forms in several stages, namely:

Stage 1 – The Trophozoite.

During this initial phase of the ich life cycle, the parasite exists on the skin of the goldfish. It has a spherical appearance, incorporating a cup shaped mouth. Present within the mouth are extremely fine hair-like formations named cilia; these cilia constantly move rhythmically inwards. They scrape tissue from the body of the goldfish, eventually transferring it into the actual mouth area.

The parasites’ presence causes the goldfish to react and create a natural barrier, surrounding it with a hard case that forms a cyst. These cysts are the most noticeable symptom of ich; giving all the indication that the fish has been sprinkled with salt.

The growth of the trophozoite depends on the temperature of the tank water; it can grow to between 0.1mm and 1.0mm wide. After a period of approximately one week, it then drops off the goldfish; then, swimming in a downward spiral to the base of the tank, it then adheres to a plant or ornament.

Stage 2 – The Tomont.

In this settled position on plant or ornament, the trophozoite then absorbs its own mouth; and creates a gel like protection around itself, at this stage it becomes known as a tomont (e.g. an encyst). This tomont then starts to replicate within the gel casing; the initial cells produced create an internal layer on the inner gel casing, the remainder of these later develop into parasites.

The number of cells produced in the tomont varies between 600 and 1000, but the most common number produced, is normally the lower figure. It will take between 8 hours and several weeks to reach this stage of the ich life cycle, the exact time scale is determined by the water temperature within the tank.

With this stage completed, the tomont then bursts, and releases its individual cells. These are now called theronts, and upon release, they immediately set off to look for goldfish to burrow into.

Stage 3 – The Theront.

These theronts are microscopic in size, and oval in shape; they are extremely good swimmers, they move around the tank until they find an unsuspecting goldfish to latch on to, and eventually burrow into the skin of the fish. Each theront then appears as a tiny white spot on the fish.

The goldfish ich cycle

They swim with cilia, and are believed to burrow into the skin of the goldfish using not only this cilia, but a combination of mechanical and chemical attacks using a pointed structure which emits a capsule of chemicals, and is found at the front of the parasite. It is only after they burrow into the skin that their mouths are formed.

The life span of these theronts is a maximum of approximately 4 days if they are unable to detect a goldfish to feed on, in the majority of cases they will perish after approximately 2 days.

What is the approximate time scale for this process?

The process is highly dependent on water temperature. The warmer the water, the sooner the ich life cycle is completed. The cycle would take approximately 4 weeks to complete at a temperature of about 20 degrees Celcius (70 degrees Fahrenheit); raising this temperature to 26 Celsius (80 Fahrenheit) would reduce the cycle completion time to about 1 week.

As the preferred water temperature for goldfish is at the lower end of the scale 16 – 20 degrees Celcius (60 – 70 degrees Fahrenheit), the ich life cycle will take much longer in a goldfish aquarium or pond.

Written by Phillyn17 (16/4/2012)