A Closer Look at Goldfish Ick – Part 1 (The Life Cycle)

Ick (also known as ich) is short for ichthyophthiriasis and is caused by a parasite called Ichthyophthirius multifiliis. This organism is a protozoan, which is a general term for single-celled animals. Although it is only made up of a single cell, it has many features that make it extremely good at what is does. In fact, ick is so successful it has become the most common disease of captive goldfish, and is responsible for more goldfish deaths than any other disease.


This is the phase of the ick life cycle when the parasite is living in the skin of the goldfish. It is a spherical shape with a cup shaped mouth at one end. The mouth contains very fine hair-like structures called cilia, that beat rhythmically and continuously inwards. These cilia scrape tissue from the body of the goldfish and pass it into the mouth.

Goldfish produce a natural reaction to the trophozoite – they surround it with a hard casing that forms a cyst. It is these cysts that are the most noticeable symptom of ick – the appearance of being sprinkled with salt.

Depending on the temperature of the water, the trophozoite grows to between 0.1mm and 1mm wide, and after about a week it falls off the goldfish. It swims in downward spirals to the bottom of the aquarium, or sticks to a plant or ornament.


Once the released trophozoite has settled, it absorbs its own mouth and secretes a gel around itself, becoming known as a tomont (or trophont). It then starts to replicate inside the gel casing. The cells produced by the first few divisions form an internal wall on the gel casing, but the rest of them develop into parasites.

The number of cells produced in the tomont can reach 1000, and will usually be at least 600. This phase of the ick life cycle will be complete in anything between 8 hours and several weeks, depending on water temperature.

When complete, the tomont bursts and releases the individual cells called theronts. These look for goldfish to burrow into.


Theronts (also known as tomites) are microscopically small and oval in shape. They are good swimmers and move about the aquarium until they find a goldfish to latch on to and burrow into.

They swim with cilia and are thought to burrow into goldfish skin using these cilia, and possibly a combination of mechanical and chemical attacks on the integrity of the goldfish skin using a pointed structure and a capsule of chemicals found at the front of the parasite. It is after they burrow into the skin that they grow their mouths.

Theronts can survive for a maximum of 4 days without finding a goldfish to feed on, and in most cases they will die after 2 days.

How long does it all take?

It all depends on water temperature. The warmer the water, the quicker the ick life cycle is complete. At a temperature of about 20 Celsius (70 Fahrenheit) the cycle would take up to 4 weeks. Raising the water temperature to 26 Celsius (80 Fahrenheit) would see the process complete in about a week.

As the optimum water temperature for goldfish is at the lower end of the scale, the ick life cycle will take much longer in a goldfish aquarium or pond.

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40 Responses to “A Closer Look at Goldfish Ick – Part 1 (The Life Cycle)”

  1. Bob Says:

    We set up r 1st tank, a 10 gal freshwater tank to raise Oranda Gold Fish. We bought 1 Red Cap Oranda, a Calico Oranda, a telescopic gold fish (not an oranda) and a Black Moor aslo not an Oranda. 3 days after we got the Black Moor he died. Petco replaced him and now we have a badk case of Ick that has all of our fich sick and lathargic. We are very concerned and believe that the Ick was introduced to the tank by the Black Moor. As a result, we have decided not to bey any more fish from Petco because the problems did not start intil we bracht the Moor home from there.

  2. cassie Says:

    not sure what’s wrong with my gold fish really worried he got frayed tail and is just laying at bottom of tank and has no appitite have also noticed some tiny black/brown dots any ideas of treatment would be much appricated thanks xx

  3. admin Says:

    Cassie, check out the articles about tail and fin rot, and black spot disease. If you think that’s what is wrong then follow the advice there. You should also think about getting a vet to look at your goldfish if you don’t reckon you can deal with it.

    Good luck. I hope he gets better soon.

  4. BOB JR Says:

    i had a gold fish tat the ick ate its tail and spread throgh out its body and i didnt eavan know what it was eather and it died and the ick killed half of my fish too

  5. Very Confused Says:

    I just happened across this sight, and I have a question about my goldfish. I have three common goldfish ranging from about 6 inches to about 8 inches (give or take, just estimating size.) I cleaned my fishtank out, boiling litereally everything before putting it back together (I had a snail breakout). The next day, the middle sized goldfish started getting lighter. about 3 or 4 days later it was completely white, and Im afraid I might have hurt it or something. Its not acting any different, and it still eats and everything. Im hoping its nothing but Im really worried, because I have had these fish 2 years, going onto 3 and I have never seen this before. Any body know what it is or if its normal?

  6. harley Says:

    i got 2 goldfish & a sucky fish 4 my birthday (march 4th). I noticed my fish had got little white spots on them and they seemed unwel. my mum got some goldfish disease safe to treat them but both of my goldfish have died and the sucky fish has now got white spots on it’s underside. i have 2 living plants in my tank & a coral rock. how should i prepare my tank for new fish as i dont wan’t any new fish i get to die.

  7. windgirlmarty Says:

    Hi, i had my goldfish for few months. One of them (Pepek) is just resting down on the leafs of plants, doesn’t want to eat more than 2 flakes and his tail is hanging down too. He’s breathing and swimming about from time to time so I ended up putting him in to separate fish bowl as other goldfish is picking on him and poking him. Now he is just laying down at the bottom of the the bowl, still breathing and saw him swimming a bit too. But it looks like he’s feeling worse… Shall I try soaked mashed peas? I have looked at all the illnesses but he doesn’t match them. Please can you help???

  8. windgirlmarty Says:

    Hello Very Confused, I have heard that fish left in a dark can get very light.

  9. kayla Says:

    Hello. I have a small pleco, small ryukin goldfish, and small black moor in a 10 gal.
    The water is cloudy but I bought some AccuClear and it’s clearing up. About a week ago, my fish got ich (but the black moor didn’t seem to have gotten it) and I stopped treatment yesterday because the symptoms disappeared about 3 days ago (using Rid Ich)
    Now, the black moor has a white cloudiness over his bubbly eyes and some whiteness on his tail and fins (especially on the edges)…now the edges are starting to fray and I think the ryukin is getting the same thing (her fins are fraying)
    What is this and how do I treat it? Can this be ich again?

  10. Megan Says:

    I bought 2 caloco orandas about three weeks ago, both of them seemed perfectly healthy and after about a week – week and a half they died. They had this fuzzy white stuff all over them and i am pretty sure it was ick. After they died I cleaned out my tank and washed everything thing with warm water and refilled my tank and used some water conditoner to help neutralize the water. I am just wondering if there is anything else i can do to prvent the ick from comming back and killing any future fish i might get?

  11. paul p Says:

    windgirl: you made a big mistake: you dont want to take a fish away from counter-fish. I know they were picking and poking him, but, that, over time, will stop. I have a comet, a large doldfish, a small calico comet, a medium black moore, and a green algae eater in a three gallion tank and they are doing fine. Also, I got a large black moore in a one gallion tank and he has ich. the only treatment i use and will use is called wardley ich-away. old school and the best. also, all fish species have a albino. i hope this helps anyone whom had a question. for ich, i fully recommend wardley ich-away. i trust it. i have kept fish all my life.

  12. Hornet11 Says:

    I have a common goldfish only an inch or maybe even smaller, i only got her the other day at petco. Today i noticed she had three white spots that looked very much like these discriptions. One on her tail (it fell off about an hour ago) one on her dorsil fin and one on one of her flippers. Shes not lathargic but shes had a very stressful week because i had to return the tank twice to buy a new one, so shes been in a few large vases i got out of a box in the garage. I’ve added the fish medicine called MELAFIX and im wondering if that will do any good? on the directions it says I’m supposed to change it after three days, but that doesn’t sound like it’ll help alot. What am i supposed to do? what can i do? and will this always be there or will it eventually go away?

  13. cynthia Says:

    The way I treat ich on my goldfishes may not be conventional but it works. I quarantine new or infected goldfish in a 1 gallon bowl (because it’s a smaller environment to control, easier to do frequent water changes and only a temporary set-up. When they are better, I put them back in my 55gallon tank).

    I use a drop of “Had-A-Snail” for every water change. I change the water in the morning, and at night for 7 days. The parasites fall off within 12-24 hours. I heard of this from a guy who owned a fish store and so glad I tried it. It also works with Flukes! Hope this helps.

  14. Zach Says:

    I’m concerned of my Blackmoore named Black Jack. I’ve had him for about a month and a half, I also have another Ryukin with him. But, I have just recently discovered 2 little white spots by his mouth, could this be Ick? If it is Ick i’ve allready purchased some Ick cure, but should i quarenitine the fish with Ick to treat him, because I have a carbon activated filter along with beneficial bacteria, or should i just unplug the filter and treat the entire aquariam?

  15. Susan Says:

    I have four goldfish in a twenty gallon tank!! I have had the tank set up for nine months now.. I have had three goldfish before this four that died back in January from ick.. I treated the water, and it was fine.. I am seeing the systems again. Cloudy water, bubbles, one of my fish is rubbing or just laying on the rocks rapidly breathing, and I noticed his fin looks ragged a bit.. Could this be ick again? I am treating it with these Lifequard tablets.. My other three fish are swimming and doing fine.. If it is ick why is the water cloudy? Is it safe for baking soda to go ito the tank to bring the bubbles down and the PH level back? Lost in thought here!! Hope you can give me some answers!! Yes, I did have two snails die recently after having them for two to three months, I also put in a new plant and changed a percantage of the water.. I need some advice of why this is reoccuring in the tank??

  16. Susan Says:

    More from above.. Can fish really go to a vet? Should I take my sick fish to the vet, if he does not improve? Seeking advice..

  17. Goldfish Ich Medications Says:

    Hi Susan,

    I’m not sure about where you live but the vets around where I live do not treat fish. They don’t know about how to take care of goldfish or fish and how to treat them. They are basically just for dogs and cats.

    From what I read above it sounds like poor water quality is causing your ich to re-occur. If the water is cloudy there is a problem. I bet you your ammonia is off the scale. You should test your water right away and do an immediate partial water change. Sounds to me like there is a breakdown in your nitrogen cycle.

    I am 100% positive that water quality is causing your ich problem.

  18. terri Says:

    My black moor is just laying at the bottom of the tank. I tried to feed him and he won’t go after the food. Today I have just noticed his eyes are a tad cloudy. He rarely swims but when he does, he is very unbalanced. I have even caught him swimming upside down a few times. He isn’t growing any tumors or fugus anywhere. help?

  19. Patricia Says:

    I have 2 gold fish about 2 years old one has a film growing over its eyes I think it is haveing difficulty seeing the other keeps facing up as though it standing on its tail.
    Can you let me know what is wrong with them as I would not keep them if they are stressed in any way.
    Thank you

  20. Jessica Says:

    Can humans or other pets like dogs get the parasite that causes ich from the tank water?

  21. Appelina Says:

    Hi! i have a Q. I bought a calico goldfish yesterday and it had the following colors: Black, orange, & white. Then today, i noticed the black spots are ALL gone! I have 6 fish: Calico, Chase (dalmation molly), Cheeto (unknowed species but small and orange NOT goldfish) Aqua (a female guppie) and my other one Apple (a regular goldfish) live with Callie my calico goldfish. Whats wrong with her?!

  22. Appelina Says:

    its a 10 gallon tank.

  23. hanah Says:

    i have a question i just bought a oranda goldfish yesterday and my fish isnt swimming he just lays there all day unless i touch him he starts swimmimg and then he tucks in his fins and sinks back down.. do u think he is in shock ?
    (i have a 10 gallon tank with litlle guppies in it)

  24. ceecee Says:

    I bought my 91 year old mom some goldfish she had one for 8 years another one for 6 I bought her a black mole and 2 placostamus they both died (yes there was enough alge for them and no amonia in the water) a few days later the 6year old calico died. I bought her 2 koi and they died right away I retested the water and everything looked fine I took a sample to Petsmart to be tested they comented on how perfect the water was 2 days later the 8 year old fish died. I bout her 4 fancy gold fish they were doing well the white one started to show signs of flip over I medicated the water and he was swimming well now all of her fish are lethargic and at the bottom of the tank the orange one is hardly ever right side up I have tried everything I can think of and can’t seem to keep her fish alive I know AI will quit buying them at Petsmart. It’s still very hard to see a 91 year old or for that matter a small child to go through the pain of loosing their fish. I whish there were some way that there could be a health requirement for selling fish in these chain stores

  25. Comet Says:

    I have a question about the ick ick disease..
    I have 4 Comet goldfish ranging from 2-3 1/2inches long. We didn’t have any problems until we bought a couple plecos. We set them up in the tank and it turns out, the little plecos do look like they have ‘salt’ on them. But it didn’t look like it affected the fish.. Until now. One of the fish now have a large ‘pimple’ looking thing on his head and I’m not sure if it’s ick ick. Because it isn’t small at all. It is white however and I am very worried if it continues to grow and get out of hand.
    I’m still relatively new to caring for them. Haven’t had them for a whole year yet but I’m worried that it might pass to the other fish. Can someone help me to find out what it is?
    I’ll also add that it is just ONE dot on his head. There doesn’t appear to be any other dots on him. The fish is white though so it’s kind of difficult to tell.
    That and I’m wondering if it would be necessary to ‘quarantine’ the fish by keeping him away from the others.

  26. Alicia Says:

    Hi, It is obvious that one of my fish has ich now that ive read this. Im pretty sure she wont make it before i can get ahold of some anti ich stuff. I just got 2 new fish yesterday and theyve been in the same tank. Do my new fish already have it? because i separated my sick fish from the new ones this morning in hopes of keeping them from getting it. ( i also put her in a smaller glass and added more Ammonia Chloramine Eliminator to the water, is that bad)

    Please help, im sick of losing more fish because im a new fish owner.

  27. Lynda Says:

    Hi, I have three little orandas which are absolutely gorgeous. I’ve read lots about them and am varying their diet and keeping the water in good condition. They all seem healthy and are swimming and eating well bit I’ve noticed that Einstein seems to rub himself against the gravel as he swims underneath the leaves of the plant in the tank. At first I thought it was a kind of game for him but now I am worried it may be early signs of ick. There are no white spots and he seems otherwise completely healthy.
    I’ve never kept fish before so I’m floundering a bit.

  28. Kendrick Says:

    I got a new redcap oranda goldfish this last weekend, and her wen is collapsing. She has a little red dot in the middle of it (her wen is orange). She is also forming blisters around this spot. She is always lounging at the top or resting on the wood in my tank. Can anyone tell me what it is?

  29. Rainclaw Says:

    We have have our two happy goldfish since Oct.`10.Our Fair fish has a little cluster on its tail,and out Store fish might have it.
    I like that image by the way [/offtopic]
    We got treatment,and we are going for a pH test soon.

  30. Kimberly Says:

    I have a goldfish that I got from a friend who moved ,she said she had him for 2yrs ,well when I took over he is now 6yrs and at least 6inches ( he is not a Koi ) Anyway I’ve read alot of the different diseases and I’m still not sure what he has ,the poor guy has got white kind of fluffy looking spot about an inch square,and I think it could be Ick but I’m not sure ,he is doing alot of things like banging his head on the glass ,laying on his side ( i thought he was showing me his silver to let me know he’s sick ) he swims normally if provoked . He is being very loving getting me to pet him and then the next minute he doesn’t want me near him) Yes he does have a wonderful personality ( not your regular goldfish)Anyway they say ick looks like salt but his kinda fluffy white ??? Can anyone HELP

  31. Jennifer Says:

    I have 5 goldfish and 2 plecos with ick. I have been treatimg them for about 2 weeks now. First I was using Ick Away, but stopped using it and started using Ick Super Cure from API. This was about 4 days ago. The first fish that showed signs seem to be clearing up some, but the others are showing more white spots now…even after the treatments. They all hang out at the bottom of the tank, as well. I was wondering what is the best direction to go now. I plan on starting another treatment but I am starting to lose hope as they are all hanging at the bottom of the tank. They are all still eating well, though. Any advice? Oh I have them in a 55 gal tank.

  32. dylansgirl Says:

    i had 3 common goldfish and ive had them for almost 2 years 1 i got from the cherry fest in whitehouse oh and the other 2 i got from petsmart and one of my fish, gummy, died and i took him out of the tank and he had little white spots on him and his eyes were glazed over and now i realized tht my other fish form petsmart, reeses, has white spots almost everywhere and his tail is frayed and idk wat it is but my 3rd fish,skittles, which i got from the cherry fest is untouched he has no white spots he still eats and he isnt different reeses is very frantic swimming around very fast running into skittles and gummie,when he was dead, and hides in this hollow plastic log thing tht i had in their tank and he rubbs and runs into this flower i also have they are in a 2-5 gallon tank if u have any advice or suggestions on what i should do or use to treat them please let me kno thank you

  33. Shubunkin jim Says:

    I have a 40 gallon tank with two mature shubunkin. (also two young shubunkin and some guppies) One of the mature shubunkin has a white film with some zit looking dots near the top of its head and gill cover. I would like to send a picture so someone could look at it. im hesitant to put her in a hospital tank as she is old (over 10 years) and dont want to traumatize her. SUGGESTIONS PLEASE. she is about 9″ long.

  34. Jamie Says:

    My goldfish has ick and I have tried meds and when I clean their tank i use sea salt to clean it and idk what else there is to do I dont want him to die cuz then my other one won’t have anyone to play with and I thought about getting a rainbow fish but idk if the will get along but should I go talk to a person at a pet store to give me advice for treating my fish so he doesn’t die i will miss him so much my fish r my best friends and my niece loves them so please help me I need it

  35. Worried Person Says:

    Hello, I have 5 little goldfishes and some of them has ALOT of little “salt” like ich. And I’m feeling very worried that others might get infected too. One has ich everywhere! I never saw them there until today. I check on my fishes every single day, but today, I see a whole lot. 3 has been infected. I think it is ICH, but I’m not sure. How can they develop that so fast? Is that bad? All of our goldfish were fine ’till today. Does ich form fast? How did my goldfish get them? Is it because of the water?

  36. silvia Says:

    Hi everybody,

    There’s a big issue with my goldfish and I need your help! Her life is in danger (I’m firmly persuaded she’s a lady fish).
    Well, she has all the symptoms of internal bacteria (popping eyes, extremely swelling belly) she gasps and breathes on the surface of the aquarium. I’m treating her with antibiotics (anti-internal bacteria from Interpret, N.9). I gave her the second and last treatment on Thursday. She’s not better at all. She has stopped feeding herself since at least 1 week.
    Please consider my other goldfish is in the same aquarium and he’s ok.
    please help me, I don’t know what else to do!!!!

  37. Steve the wonder fish Says:

    Very confused: I know it’s been years since you posted, but just for the sake of others who read this, goldfish can change colors and be perfectly fine. My first goldfish was actually won at the fair, when I got him he was a black tiny little thing and about a year or so after getting him he turned a bright brilliant orange. He lived to be 5 years old, which is extraordinary for a goldfish won at a fair. Just proof that a fish can turn colors and still live a long time.

  38. goldfishwoner Says:

    Just read all the post. Too bad no one answers them. These are very good questions. Please, someone with knowledge (maybe a vet) please answer these question even if they are years old. Please, for the sake of those who experience the same problems!!!!

  39. easterchickenz Says:

    I bought a suckerfish from petsmart a couple days ago, I have a 10 gallon fresh water fish tank that I have 2 small rykin fantail goldfish and a small catfish already in the tank. Well now my goldfish appear to have cloudy looking tails. They aren’t really white spots on its tail but I am wondering if the goldfish have “ick.” The goldfish are also spending more time sitting on the bottom of the tank. Please let me know what it is and how to treat it.

  40. Joyce Says:

    My goldfish that I’ve had for almost two years has developed ick…Everything was fine until I bought a live plant at Pet Supermarket last week…From what I read here, either the purchased plant brought the parasites with it or its the water “quality”…I have experienced cloudy water on occasion… My question, if anyone with experience will answer is this: What kind, specifically, of bottled spring water do you buy? Also, where is the safest place to purchase new fish? Like I said, everything seemed to be fine until I put a live plant in the tank! I will not do that again… I will check back to see if there are answers to my questions…Thank You!

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