It is a setup where I stock the largest Australian native fish predator, the “Murray Cod”. I have a few fingerlings in the fish tank with 2 silver perch, a little yabby and some fresh waterclams. bending on the top of the aquaponics tank, I watch the fish. one of them appear closer and I see a multitude of white spots on the skin and fins of the fish! Yes this is the white spot fish disease and it’s spread on my aquaponics fish…

What means “White Spot fish Disease” in aquaponics

Also known as Ichthyophthirius, this parasite is very common. It is very different to the prawn white spot which is a virus. Ichthyophthirius has a complex life cycle. The visible spot on the fish is called “trophont”. It is encysted and feeds on the fish.

The impact on the fish

This parasite literally eats the energy of the fish. Even worst, the trophonts fixed on the fish gills disturb the capacity of the fish to absorb oxygen. If nothing is done, the parasite will multiply until the fish die of asphyxia.

How does the parasite spread and what is the life cycle?

White spot has a complex life cycle. It can come from a variety of sources such as new fish, new aquatic plants… Once in the water, the larvae called “tomite” will fix on the fish surface. They can fix on the skin, the fins or the gills. Then, they form a cyst on the skin of the fish. When in a cyst form, the parasite is protected and can’t be killed. The cyst will remain attached to the fish for several days and then fall. There, it will fix itself on the bottom of the tank until it maturates and gives birth to thousands of little larvaes. The whole cycle can take from 4 days at 25C to 30 days at 10C.

How can we get rid of the fish disease in aquaponics?

Ichthyophthirius is only vulnerable under the larvae form. aquaculture and aquariums use a multitude of products such as: Formalin, malachite green, methylene blue, potassium permanganate…

In aquaponics we will not use those products as our bacteria would die and the plants would possibly accumulate the chemicals.

Instead we will starve the parasite larvae. We remove the fish from the aquaponics system. If the Ichthyophthirius larvae don’t find a fish in the few days following their birth, they will die.

In this video I show you how I remove the fish from the tank and increase the water temperature to 25C. It increases the parasite cycle and complete the full loop in less than a week. I leave the aquaponics system in those conditions for 3 weeks. without fish we can comfortably assume that all parasites will die.

Regarding the fish, I keep them in a separate tank with 5g/L of Salt and I change the tank every week to make sure new larvae will not appear. After few weeks, the white spot will fall and the fish will be healthy again. More information on handling fish disease there

You will probably be interested to discover Jonathan’s six steps to build and manage an Aquaponics system. Click here to access for free! Thanks and good reading 🙂