ALL THINGS KOI AND H2O
By Duncan Griffiths
is a common fresh water parasite with many genus spread across all corners of
the globe, with the best-known genus being C, Cyprinii.
In salt water fishes it has counter part called Brookynella equally as deadly
Chilodonella is classed as a motile ciliate protozoa that will graze on epithelial cells of the gills and skin, described as heart shaped, but the best description of the shape I ever read was "leaf" shaped for me this sums the description up.
It measures approximately 50 microns by 40microns and can easily be seen at x 150, although it is one of the more tricky parasites to recognise, seeming to blend into its surroundings a little morethan most parasites, although described as motile its movements are not as rapid as most other parasites I.E. Trichodina or Costia but once you know what it looks like in reality, it is easier to spot.
Staining a slide with Methylene blue may be of help if you have never seen this parasite before.
Note: Chilodonella leaves the host immediately after death of the host occurs, so you will usually not find it upon examination of a dead fish specimen
As mentioned its shape is like a broad leaf with a little dimple in the posterior broader end. When viewed under a microscope it's fairly transparent to an untrained eye. Chilodonella has a nucleus in the lower third of the body with a micronucleus inside.
It is flat on the ventral side and convex on the dorsal side.
The cilia is on the under side with the top having no cilia at all. The mouth is also on the ventral side with an oral groove
Chilodonella reproduces by binary fission or occasionally they will join together to reproduce this is called conjugation, where they may share genetics, as with a lot of parasites Chilodonella can and will lie dormant until conditions become favourable, I.E. the koi gets stressed with poor water conditions or some other disease, then it becomes a serious adversary and mover, with an optimum temperature range of between 5-10 deg c, giving them a significant head start on the koi's immune system coming out of winter in early spring. When presented with the right conditions and opportunity chilodonella can reproduce at an alarming rate, and quickly over come a koi
Typically it's not uncommon to find this parasite on a weak koi suffering from other ailments, and as with Costia this would not be considered unusual thing to see under a scope, but remedial, actions/treatments should be put in place as soon as is possible to prevent any outbreak, but in heavy infestations it is unmistakeable in the symptoms it presents.
Fish begin to breath laboured become very lethargic, clamped fins and spend lots of time at the surface gulping air, usually head up at the surface with the body looking down into the pond at an odd angle with instability in there swimming motion, you may even be able to push them over, and above all horrendous amounts of thick mucus are produced, coupled with secondary bacterial infections in the later stages of the disease.
It should also be noted if this parasite gets a foothold some of the koi may not make it through any and all treatments, as some koi will be severely weakened.
Treatments are many but in the past I have found chilodonella more than able to resist quite a few, in particular and surprisingly, Potassium Permanganate, successive doses rendering no effective cure in lots of clinical cases, unless used in conjunction with salt, but I must confess I'm not a huge fan of the using of Potassium Permanganate with salt. Chilodonella may respond to PP used on its own on the odd occasion. Chloramine T, Acriflavine and other chemicals also have limited sporadic success
As with white spot one treatment stands out head and shoulders above all others:
Malachite green and Formalin used simultaneously
I have yet to hear of a case of chilodonella that has not to succumbed to this treatment usually in single dose or two doses a week apart, so while other medicines do have there success with this parasite, if you want to nail this critter and nail it fast and get it every time, my personal choice would be Malachite green and Formalin.