You assume this - but you can´t be sure. There can be other explanations that could be as likely as this was the fish that bring it in. Everybody assume that the dormant stage of the ich parasites only can be 72 days - not longer. This 72 days is based on one investigation and only show that the parasite can be dormant at least 72 days. Not that it is the maximal dormant time. Knowing something about parasites and their way of surviving time - I would not be surprised if ich parasites could be dormant for years. My background is fish farming. In an recirculated eel farm we had problems with flatworms from the genera Dactylogyrus (your common name for these is flukes and in this case gill flukes) In the beginning – it was enough with formalin treatment every third to second week. – this become down to lesser than 1 week. This flatworm is an egg layer and the eggs hatched in our biofilters. We developed a method with an anthelmintic (if I remember right – it was Fenbendazole). We use a second treatment after known period of hatching and in order to be safe – a third just after the second. It works for 2-3 months – suddenly new parasites start to hatch with much longer dormant stage than previous known. This say two thing – flukes can develop and stay in closed system and you can´t have a safe period.
An observation QT is effective in this case. If the fish have one or two parasites you miss. It will be between 200 and 400 in a week and between 40 000 to 80 000 in two or three weeks. This you will notice. TT in 7 to 10 days is also effective in this case.
And let us put it this way – if you have not prophylactic treated your old fishes, don´t try to extinct the system from pathogens – had one or two ich parasites caused this outbreak?
During the last 15 years – I have helped a friend of mine and around 20 000 (or more) SW fishes have passed my hands – direct imported from Asia and maybe 2 – 3000 fish from other European vendors and some from the US. Brook and ich have been the diseases I have seen. Never ever seen any flukes – and not velvet. We never treat prophylactic – just observe and treat if needed. Ich is treated with copper and brook is so seldom that a fast sorting out of infected fishes helps. My friend’s system have two very effective UV-C (TMC manufactured pro systems) and he run a little bit lower salinity. Its all. In my SW aquaria I have seen ich once (in two clowns) Solved it with taking out the two with symptoms and run TT (or in my case BT – bucket transfer method) and run rather much ozone in the main display for three weeks. Never come back – and there was a tang in that system!
Nowadays I always let my newcomers be in my refugium for 1 to 2 weeks in order to just relax and have a smooth transfer to my DT. With this way of handling – they also get the same smell as the other fishes and I have notice that much of the earlier bullying has disappear. They also get a stress-free environment and that favour their possibility to adapt to the microorganisms of my DT – without being sick. If I should run an observation DT – it would be in a normal aquarium with hiding places and a few other friendly fishes and I would do WC with help of my DT water. This will be as a slow vaccination
Sincerely Lasse
