Goldfish Care Tips

A Free Monthly Resource For Goldfish Enthusiasts
May 2025
Issue #137

In This Issue
Fancy Goldfish Growth Rate

The rate at which a Goldfish grows depends on several factors, such as water mineralization, water temperature, and food, so how fast will a fancy variety grow if given the ideal conditions?

Fancy Goldfish Growth Rate

5 month old 80mm Black Moor

I am often asked, "Why are my fish not growing?".

I can understand the question because, as I explained in the November 24 issue #131, Goldfish Growth Secrets, I had the same issue.

I mentioned I was running two experiments that I thought eliminated all possible reasons for a Goldfish not to grow. These included:

Water mineralization (my water is extremely soft)
Feeding portions
Frequent water changes

Black Moor Juvenile Found

The fish in these experiments are over twelve months old and aren't ideal candidates. However, in late January of this year, I found a Black Moor juvenile in a container I had moved duckweed into from the adults' pond before setting the pond up for spawning.

I estimated by its size, and because it had no eye development and was still uncolored, it must have either been a newly hatched fry or still in the egg when I moved the duckweed on December 31.

Although only a few inches deep, the water was teeming with daphnia, so this fish had had an ideal start.

Experiment Number Three

I started another experiment using this juvenile fish to see how fast a fancy Goldfish would grow given ideal conditions.

Usually, when I am growing out fry, there are hundreds or thousands of competing mouths for the food available, and I don't feed them continuously, usually one feed in the morning and one in the evening.

This was a golden opportunity to test the growth of a young fish kept on its own.

I moved the fish into a 50-liter aquarium, heated the water to 26^oC, and fed heavily.

As you can see from the image above, as of May 31, the fish at 5 months old is 80mm in body length.

This is the fastest I have ever grown a fancy, deep-bodied variety.

Yes, some will say growing a fish that quickly will shorten its life and affect spawning performance, but this is a juvenile fish, and I don't heat my adults, so this fish will experience little growth over winter and will grow at a rate temperature dependent from now on.

Experiments Two and Three

My two other experiments were with two undersized Celestials and four Black Moor.

The Celestials were 50 mm runts from a spawn in Oct 2023. After 5 months of testing, they had grown to 73 mm and seemed to have stopped growing, a similar story for the Moors.

Since aligning water temperatures and feeding portions closer to the juvenile Moor experiment, they have grown approximately 8 mm a month. The Celestials measure 95mm as of May 28, impressive growth for fancy adult Goldfish.

Conclusions

When all factors needed for fast growth are brought together, particularly water temperature, Goldfish will grow large quickly. Some Goldfish keepers are fortunate to have, literally on tap, highly mineralized (hard) water and live in a temperate climate.

All they need to do to grow their Goldfish large quickly is keep water quality high and feed around 2% body weight daily.

If your fish aren’t growing, there will be a reason why.

Comments? Ideas? Feedback? I'd love to hear from you. Just reply to this e-zine and tell me what you think, or what topics you want to be covered.

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