How to Get the Little Goldfish Through Winter?

by Annett
(Germany)

Hello,

I have a question about overwintering my goldfish. Specifically, it's about the offspring born this summer. In the past, we have always overwintered goldfish in large containers/barrels in the cellar - unfortunately, the pond is not deep enough to guarantee their survival outside.

Wintering in the cellar always worked well for the large goldfish, but the small ones often didn't survive the winter. Everything went well for the first few weeks, then one after the other died. Only a few lasted until spring.

I would like to change that. What conditions do small goldfish need? Should they be fed occasionally or not? (So far we haven't fed them - neither the big ones nor the small ones).

---

Grant’s Reply

Hi Annette

Juvenile Goldfish (under 12 months old) do find their first winter a problem in colder climates if they are small. The usual reason is because they haven’t acquired enough body fat during autumn to last them the 3-4 months of winter when food is scarce or, the water temperature is so low that appetite is suppressed.

In my latest e-Zine I discuss pond overpopulation and how it is dangerous for the whole pond population if they go into winter under-fed.

So, let’s look at the best way of ensuring the young ones survive.

I assume you keep the young fish separate from the larger ones.

As I mentioned in the e-Zine, any young fish will generally not grow to their potential in a pond environment, meaning they will be undersized.

A juvenile fish can easily attain a size of 75mm body length in a season if conditions are good. At this size they would have enough body fat to last the winter.

Any fish under this size means conditions were not optimal for the new offspring over summer/autumn.
I am assuming your fish are under 75mm. I will also assume they wouldn’t have much body fat because of feeding competition.

As they have been in a pond with adults, it can be assumed they are carrying parasites which are a problem to fish under 50mm, especially in a crowded environment.

Steps for Wintering Juveniles

By my calculation, you are in mid-autumn.

Step 1. You need to separate out the juveniles now so you can start feeding them heavily and treat them for parasites. I don’t know what is available in Germany but you need a Praziquantel based medication such as API General Cure, PraziPro, ParaGuard or something similar.
Step 2. You need to monitor the water temperature with an aquarium thermometer. When temperatures start dropping to around 10^oC, monitor feeding activity. Some fish will feed, others will show little interest in food. This includes the adults.
I generally don’t feed below 10^o, and recommence feeding small amounts around 12^o.
Step 3. Monitor water quality.
You don’t mention whether you run filters in your containers. If you don’t feed the fish, water quality is easier to maintain. Feeding the juveniles will require the water quality to be monitored closely. A properly cycled filter stops ammonia spikes which are fatal to fish.

Use a water test kit such as an API Freshwater Master Test Kit to check for ammonia and nitrites which are toxic to fish. When nitrates reach around 40 ppm (parts per million), a water change is required.

If your fish are particularly small, say around 25mm, consider heating the juveniles to around 15^oC.

By taking these steps, there is no reason this season's juveniles should not survive this winter.