Quarantine and Introducing New Fish
Introducing new fish to your pond is an enjoyable activity and provides some of the best bits of fish keeping. Unfortunately, no matter how reputable the source of the new fish is, introducing new fish will always come with a risk. Thankfully there are several ways you can reduce the risk of this happening.
Quarantine
It will come as no surprise that the most influential way to protect your fish and prevent the introduction of unwanted pathogens to your pond is to utilise a quarantine facility. The quarantine doesn’t need to be overly fancy but as a minimum it needs to be a completely separate system to the main pond with its own filtration as well as separate equipment such as nets and bowls. There can be no shared water flow.
It is advisable to keep quarantine running even when not in use. This is beneficial when fish suddenly fall sick and need to be isolated quickly. If quarantine isn’t set up and running, this will not only cause delays but you’ll have to battle water quality issues whilst you get the filtration system up and running again, which will take up to 6 weeks.
For this reason, it’s much better to continuously run quarantine facilities. You may need to keep some small fish in there permanently to keep the biofilter running effectively.
Once your new fish are introduced to quarantine, they need to spend X amount of time in quarantine before they are introduced to the main pond. The length of time a fish needs to stay in quarantine is variable and is dependent on water temperature. This is because at lower water temperatures it takes longer for disease to appear.
For water temperatures 17 degrees and above, I recommend a quarantine period of 3 weeks (minimum) and for water temperatures under 17 degrees, 4-6 weeks.
During the quarantine phase keep and treat the fish like you would in the main pond. Feed sparingly initially to allow them to get over the stress of transport and then gradually work this up to their normal ration. Watch the fish carefully for any signs of external disease. Look at the health of the skin and the fins as well as the eating and socialising behaviours. If disease is suspected start by performing skin scrapes or reach out to London Aquatic Veterinary Services for assistance.
Watch the fish carefully for any signs of external disease. Look at the health of the skin and the fins as well as the eating and socialising behaviours.
Screening for Parasites
The main purpose of holding fish in quarantine is to reduce and exclude the risk of introducing disease such as parasites to fish in the main pond. The most common way parasites are introduced into ponds is via the introduction of new fish, so by utilising a quarantine facility first, this risk can be counteracted immediately. Thankfully parasites are usually relatively easy to deal with and carry a good prognosis once diagnosed.
As there is only one parasite in fish you can see with the naked eye – Argulus foliaceus ‘Fish Louse’ you will need to scrape a selection of incoming fish for parasites using a microscope. You can do this yourself or you can enlist London Aquatic Veterinary Services to help you with this. If parasites are found on skin scrapes then you will need to treat all fish in quarantine with a suitable antiparasitic. Make sure to scrape again at the end of the treatment course to confirm whether the treatment has been a success.
So you can see, by scraping fish on entry into quarantine, you have not only prevented the introduction of parasites into your pond but you will have also likely saved money by treating quarantine only and not the larger volume of the main pond.
It also means you haven’t unnecessarily exposed healthy fish to anti-parasitic medications.
Other Pathogens
Other pathogens to be aware of include viral and bacterial infections. It is particularly important to allow enough time to pass in quarantine at low temperatures for these diseases to become apparent. Classic symptoms of bacterial infections to look out for include fin rot and erosion, ulceration, dropsy (protruded scales, swollen body cavity and swollen eyes).
Viral infections can be harder to detect. Symptoms are varied but can include weight loss, listless behaviour and necrotic changes to the gills (often seen as white and grey patches on the gills). Thankfully, Koi Herpes Virus, the most feared fish disease in the UK can be tested for prior to purchase. In fact, most high-quality koi coming from Japan will have already been tested and verified as KHV free before importation. Ask your koi dealer about KHV control and testing if you have any questions.
If no testing has been performed London Aquatic Veterinary Services offers non-lethal screening services. Swabs can be collected from the gills of fish and sent to a specialist lab for PCR testing, to confirm KHV status.
Introducing New Fish
Once the allotted quarantine period has elapsed and provided the fish are:
Free from external disease
Eating and behaving normally
Clear of parasites on skin scrapes
Then you can start making plans to introduce the new fish to main pond.
If you have a lot of fish in quarantine making the move over to the main pond, introduce the new fish in stages so as not to overload the biofilter with a sudden increase in bioload. You may need to leave 1-2 weeks in between batches. Test your water quality weekly and use the results to guide you on how the biofilter is coping.
Although you can introduce new fish at any time of the year, it is advisable to introduce new fish in Spring when water temperatures are warm enough to support the immune system. Following on from this point, it is a good idea to support the immune system of all the fish following new introductions. For koi and goldfish this can be done by feeding Yugen by Takazumi for 5 days and by dosing the pond water and food with vitamin C*.
*Please seek guidance from London Aquatic Veterinary Services before treating the pond with vitamin C.
