Immaculate Conception!

by Jane
(Kent, United Kingdom)

Hi there, my parents had two goldfish in their outside pond for quite a few years. I think they may have had some young ones, but they didn't survive. One of the main goldfish died about 5/6 years ago, so we were left with one.

In the spring this year we noticed some, what looked like, small black (and one white) fish. We were dubious and thought maybe tadpoles or newts, but they have turned into little goldfish. currently about 1-2" long, some have turned gold, some are black and gold, and one white and gold. It's hard to say how many there are, but at least 10.

I can't really find anything online about this being a thing, goldfish having fry on their own.

Unfortunately the mumma fish has now died, so perhaps she knew her end was coming and cloned herself?

Would be very interested if you have come across this before.

Many thanks
Jane

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Grant's Reply


Hi Jane

You haven’t read anything on the Internet, because Goldfish are not known to be able to self-reproduce (asexual reproduction).

Some fish I believe can, but I have no evidence Goldfish do, although recently I read a scientific paper that claimed Goldfish can use the sperm of another fish species to fertilise their eggs. I suspect this has come about because Koi carp and Goldfish are known to interbreed, as do other carp species.

What I believe has happened is the original pair did breed successfully, but because of the limited amount of food in the pond the fry have remained small, and uncoloured.

As they have slowly grown, and started to change colour, you have noticed their presence.

Another option is the original pair bred successfully, but very few fry survived and remained uncoloured, therefore unnoticed by you.

Goldfish become adults after 12 months, whatever their size. (I have bred males with a body length of little over 25mm (1”).

These few that survived have bred with the female, and their fry have been more successful at escaping predation, and are the fish you are seeing now.

If you see a one or two of the fish that are larger than the rest, especially if they are uncoloured (grey), this would indicate the latter option has occurred.

I have a similar situation in one of my ponds where about 15 juvenile fish are present.

One of the juveniles is much bigger than the rest, (50mm) and I suspect he escaped my clean-out last season and has bred with the one female in the pond this season.