The Tragic Tale of Ichthyopthirius multifiliis’s Invasion of Bana Bavis

by KR

Remember those rainy childhood days where you would spend hours upon hours playing Fish Tycoon? Just me? Okay. Well, if you do recall, the absolute worst part was when you noticed the white globules of death on the sides of your fish (Figure 1). Ich. Then it happens. Your fish dies because you were unable to afford the treatment because no one wanted to buy your damn Canary Arrowfish!

So how did this happen? How did your poor fish, let’s call him Bana Bavis, get Ich? He was so young, only a few days old in Fish Tycoon time, yet he had so much promise. And now, because of Ich, he’s dead.

Figure 1: Bana Bavis and his Ich.  1A refers to what Ich looks like on a fish

in Fish Tycoon.  The white specks near the tail is where the infection took place.

Picture courtesy of a young teenager that has nothing better to do than play Fish

Tycoon upon request. 1B shows Ich on an actual fish.  Picture found at here.

This disastrous disease in freshwater fish is caused by an evil eukaryotic microbe called Ichthyophthirius multifiliis. Ich parasitizes fish, both in the wild as well as in aquariums. It is especially dangerous in enclosed environments because it’s able to circulate and infect more undeserving fishes. After infection, the poor fish victim often displays symptoms including loss of appetite, abnormal hiding, rubbing against objects, droopy fins, and fast gill movement. The fish also tends to have white spots on the skin or gills, which is why Ich is often referred to as “white spot disease”.







In order to gain a more complete picture of this infamous parasite and how it infected and killed the innocent Bana, it is important to understand its life cycle and the terms attributed to the various aspects of its life cycle (Figure 2). When the Ich is in its infectious form, it is known as a theront. The theront gets under the fish’s skin (literally), and develops into a trophont. As a trophont, the Ich is able to feed on its unfortunate victim and grow—causing the white spots to form that are indicative of the nearly unavoidable, imminent death. After the trophont exits the poor fish, it is known as a tomont. These nasty tomonts are able to swim for a brief period of time until they adhere to something in the surrounding area. They then secrete a capsule around themselves and comfortably reproduce inside. These capsules can form hundreds of tomites, which when released, become the infective theronts in 18-24 hours. The dastardly theronts are then able to infect new prey; however, if they don’t find a new victim within one or two days, they will die. That being said, the successful theronts that do find new targets are able to start the infection cycle over, and the resulting number of parasites produced increases by 2-3 orders of magnitude with each round of infection ¹.

Figure 2: Life cycle of Ich.  This shows the different life stages of Ich
and the associated terminology. Picture from here.

Taking this information and applying it to Bana’s situation, poor Bana was innocently swimming around when the evil I. multifiliis theront struck. But how did I. multifiliis find Bana? The theront can only live for a short time in the water, so how was it able to find and invade Bana? This is where things take an even more depressing turn. There is no one to blame but Bana himself. A variety molecules that are produced in Bana’s own mucus and blood actually attract the theront to Bana. The theronts are able to detect these molecules and swim towards them. Though it is not entirely certain what specific molecules in the mucus and blood are to blame, it seems that villainous theronts are attracted to high molecular weight proteins that are found in these bodily fluids³.

While the theront was approaching Bana, the devious theront discharged the contents of one of its organelles called a mucocyst. The theront was then coated in a sticky discharge. This disgusting discharge helped the theront adhere to Bana’s gills. As the theront began to penetrate, Bana’s cells surrounding the area of penetration began to die ². It only took five minutes, but the theront successfully invaded Bana and entered the trophont stage of life. The carnivorous trophont then eats at the remnants of Bana’s cells and begins to grow. The trophont continues to grow and the characteristic white spots of Ich begin to appear. Now you know for sure something is wrong and you begin to worry for Bana’s young life. He must be quarantined. The Ich gets worse and worse until the tomonts escape. Bana now has an open wound covering areas of his skin and gills, which ultimately leads to his demise.

This ends the heartbreaking tale of Bana and his fiendish Ich. At least Bana Bavis died the way he lived… Tragically.

References:

1.        Buchmann K, Sigh J, Nielsen C., Dalgaard M. Host responses against the fish parasitizing ciliate Ichthyophthirius multifiliis. Vet Parasitol. 2001;100(1-2):105–116. doi:10.1016/S0304-4017(01)00487-3.

2.        Movement C. (Ciliophora) Invasion of Gill Epithelium. 1980;(5):208–212.

3.        Buchmann K, Nielsen ME. Chemoattraction of Ichthyophthirius multifiliis (Ciliophora) theronts to host molecules. Int J Parasitol. 1999;29(9):1415–1423. doi:10.1016/S0020-7519(99)00091-0.