Ichthyophthirius multifiliis

Ichthyophthirius multifiliis

Ichthyophthirius multifiliis in Freshwater Aquarium Fish is a ciliate an single celled external parasite and can be most stubborn to eradicate due to its multi stage life cycle, but its life cycle is predictable, so timing is key to success.

Lets paint this picture of ICH!

  • Find a host and hold on.
  • Burrow in and start constantly turning and churning between the skin and flesh.
  • Feeding on the remnants of the destroyed skin cells and body fluids for 10-20 days,
  • Irritating the skin, thus stimulating it to grow and cover up to protect it,
  • Large pieces of skin and flesh start to disintegrate as its eaten.
  • Once Grown the parasite lets go, swims away looking nest to reproduce,
  • Forms a protective cyst, then starts cell division for 8 to 24 hours, 2, 4, 8, 16, …….
  • Once time is up and there are 1000+ swarmer cells ready in each cyst, then
  • They SWARM out hunting for a new host, they only have 48 hours or die.
  • Even during swarming they reproduce by cell division,
  • Fish must be living for them to host, once dead they all leave and enter cyst stage,
  • Except the very young ones, they enter a permanent resting stage for many weeks,
  • They remain viable, lurking, waiting for a new host to come by.

BOO, got ya.

Below is the format overview we follow and how we present the information.

UPDATED: July 3, 2026

Identification

Small white dots, looks like salt on the fish.
Rubbing and scraping themselves.
Lethargic and apathetic.
Lesions
Skin desintigration

CLASS

Protozoa

Reproduction

3 stages, can only be killed in one of the 3 stages.
They can lay dormant in wait in your aquarium for many weeks.

Causes

Fish stress reduces their defenses allowing infection.
Bacterial infections soon attack the open wounds.
Poor water quality and poor husbandry foster the outbreak.
The fish are at risk from starvation, malnutrition, improper diet, incomplete diet, cold, stress from transport and when unsanitary condition in the tank that burden their processes.

Treatments

PJS ICHKIL is a formalin and malachite green solution, 10 days minimum.
Temperature increase for 3 weeks minimum,
This will speed up the life cycle and will drive to uniformity.
Hypo salinity change
Salt NaCl can irritate them and help the host push them off.

Observations, Notes, Remarks

Complete all of the treatment routine, ever time!!!
In a sense need to build a wall - that no living of target organism gets past this point. Then allow the life cycle to run into the wall.
Good news is there seems to be an immunity that can be built up if fish do survive, but it seems to be specific to the ones in your own tank.
New fish when introduced are not immune to your specific tank of critters, so they may have a break out, while the rest of your fish are fine.