Received my aquabiomics edna test results. They found ich in sample. I had ich in my tank but after fallow period never had any signs for more than 6 month. I have a baby hippo tang which is known for being extremely sensitive to ich but no signs at all as well as other fish. Should I be worried?
A few thoughts on this questions:
Should I be worried?
The report shows your sample was about 0.15% Cryptocaryon. Thats something like a dozen identical DNA sequences matching this parasite better than any other known organism. In terms of the raw data, this is a convincing signal that it was really in your sample.
How could it get there if its not really in your tank? Well, cross contamination would be one possibility. I checked and there are only two other samples in that batch that showed Cryptocaryon, and they have different DNA sequences (different types or populations).
Based on these data I think its really in the tank. I'll also add that this level is similar to what I see when I introduce a single infected fish in an experimental tank.
Should you be worried? In my experience you can have an infected tank where the existing fish are OK, but the next fish you add may not be. Theres a lot of strategies where to go from here, this forum is a rich source of advice on that topic. But in my view, your data are convincing enough I'd consider it a tank with a hidden population of Cryptocaryon.
How long does DNA last in aquariums?
I wish we had better data on this point. In the eDNA literature people often just wave their hands and say "perhaps a few weeks". The real answer is almost certainly "it depends on a lot of things", and its probably not possible to give a precise number. But its certainly not years. its days to weeks.
Recent studies estimate that eDNA persists for times rang from a couple days to a few weeks:
Rupert A. Collins et al. show that environmental DNA degrades faster in the inshore urban environment than the ocean-influenced offshore environment. This study suggests that environmental DNA can be reliably detected for two days, providing an optimal time window of high local fidelity.
www.nature.com
Anthropogenic disturbance in natural environments may cause unfavorable habitat conditions in which old species are lost, or new species are introduced. These interventions could affect biodiversity. However, rapidly advancing environmental DNA (eDNA) methodologies can be used to recover...
link.springer.com
Of course thats in the ocean, what about in aquaria? I've recently done some experiments with adding fish - you can see their DNA within 48 hours. When I finish these experiments I'll remove the fish and monitor disappearance of their DNA. I bet the answer is that within 2-10 days it will be undetectable.
But lets certainly acknowledge that eDNA sequencing can detect DNA from organisms that used to be present, but are gone now. The higher the level, the less likely this is the case.
Some say Ich is present in all systems
I agree this has been said a lot but data don't support the claim. Its common, showing up in about 12% of tanks we've tested.
With that said I've certainly seen plenty of cases, including one of my own tanks, where Ich persists at measurable levels and the existing fish are fine without taking any special action. So I think theres good evidence to support that claim that you can manage an otherwise healthy tank with Cryptocaryon present. I just don't claim to have any special advice about how to do that. My own approach, in my one case, is I'm not adding any more fish to that tank until after I clean up the ich (sometime in the future)
