A week of Goldfish Eggs and Fry

In January 2010, I bought two comet goldfish for our little pond. I quarantined them in a small tank in my kitchen, where, to my surprise, they bred.

One morning, just before dawn, I woke up to the sound of splashing and trotted through to the kitchen, expecting to rescue flopping fish from the floor. Instead, what I found was two sheepish-looking goldfish, huddled together at the back of the tank. They looked exhausted. There was a pale milky color to the water and the tank was covered in tiny spheres.

Above: Day one - Healthy eggs are clear, whereas unfertilized and unhealthy eggs turn white. 
The eggs stick to everything. The milky quality of the water is from the spawning.

I quickly removed the adult comets from the tank and declared quarantine to be complete. I popped them in the pond and then lowered the level of water in the fish tank to about halfway. (I remembered reading something about the weight of the water crushing the goldfish eggs. I'm not sure if it's true, but I decided not to take my chances.)

Above: Day two - Unfertilized eggs tend to grow fungus on them. This can spread easily to other eggs, so daily water changes of about 25% are essential for the health of the remaining eggs.

By day three I could see the fry inside the eggs. I spent hours watching them and photographing them. It really is a special treat to watch a creature come into existence. They grow up so fast...

Above: Day three - The two bulges to the left are the eyes. The body curves around the inside of the egg, clockwise.

Day three and four - Getting restless. The goldfish fry start turning and wriggling inside their eggs.

Above: Day four and five - The fry's tail emerges from the egg after much wriggling and squirming. Within moments, the fry has swum free. It happened so quickly that I missed it. The second photo shows the now-empty egg shell.

Above: Day five - Swimming vertically and attaching themselves to the glass. The mouth hasn't properly formed yet, and so the fry feed off their yolk sacs, the bulge in the region of the stomach.

Above: Day six - The swim bladder and the mouth have started to form, and the fry are able to swim horizontally for short stretches of time. You can see the tiny fins in this picture.

Above: Day seven - Tiny baby goldfish! 

For the first week, the fry live off of their yolk. In the second week, I began to feed them on a home-made mush that I called "Fry Paste". This ominous-smelling mixture was made with a pinch of goldfish flakes, half a boiled egg yolk and 3 well-cooked, shelled peas. I mashed it all thoroughly and stored it in a small jar. Twice a day I'd put the tiniest smear on my fingertip and rinse my finger in the tank water to allow the food to dissolve into the water.

On the first day, I counted about 120 eggs. By the second day, only 70 were still healthy. After the eggs started to hatch, I counted 55 fry, and lost about 5 per week after that. I had two fry that were larger than the others. They were stronger, faster and much, much meaner. They ended up eating most of their siblings. I now have... Four goldfish.

Above: The main culprit, with his usual "Who me?" expression.

Above: Survival of the fittest. The largest fish (left) is genetically superior to his siblings. Of all the fry, he alone had no physical abnormalities. I think the majority of the fry came out deformed because the parents were still young.

I wouldn't take up goldfish breeding as a hobby, but it was a very interesting experience to watch the fry develop.

Thinking about Breeding Goldfish?

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