Fortunately, I had only recently started treating the pond with a Formalin and Malachite Green anti parasite treatment so my Ranchu have been returned to endure the treatment. Several hours in and everything appears to be normal. All fish active, breathing well and looking for food. Let's hope that the previous Gill Flukes and Costia have not caused to much damage to the gills and the fish can cope with the course of treatment.
I have researched a lot and read many conflicting recommendations regarding the preferred treatment for Ranchu, these included baths in salt upto 20g per litre, Potassium Permanganate, and Formalin and Malachite treatments all appearing to have varying results. Having some immediately available, and in an attempt to treat the issue as soon as possible, i've gone with the F&MG treatment.
A couple of tips that may be useful that i have discovered whilst using the microscope:
- I actually had difficulty in locating Costia (notoriously small) using a cover on top of the slide (as is generally recommended). I think this was due to everything being forced into a much flatter area and fluid for the costia to move in being limited. My best results came without the use of a cover. The scrape went straight onto the slide, and a drop of tank water onto that. This gave a good depth of water on top of the scrape which gave the parasites lots of space which made them far easier to spot.
- Costia will also often appear and move quite differently to examples found on the net. There were many examples i viewed where they moved in a very controlled manner, not always in the "erratic" movements described so often.
- I was able to identify Costia with as little as 100x magnification, although my eyes are pretty sharp. Above 400x provided a much clearer identification (in particular the more familiar comma shape).