Goldfish Care Tips

A Free Monthly Resource For Goldfish Enthusiasts
November 2024
Issue #131

In This Issue
Goldfish Growth Secrets

Some Goldfish keepers have the problem of their fish outgrowing their aquariums, while others are struggling to get their fish to grow at all.

Goldfish Growth Secrets

30 gallon tank with 3 feeder fish after 12 months

A post on Facebook the other day reminded me of the problem some of us have growing on juvenile fish into reasonable sized adults in a reasonably short timeframe.

It is frustrating when some readers show me pictures of enormous fish in small aquariums that have to be given away because they have grown so large, and I have others complaining that despite heavy feeding and maintaining high water quality, their fish either don’t grow, or are very slow growing.

I fall into the latter group, with slow growing fish. My fish are housed in both aquariums and ponds, and both groups are slow growing. If the fish population is very low, for example 1 fancy variety per 100 liters, with filters, my fish will slowly attain a reasonable, not large, but reasonable size.

Some will argue that yes, this is what we are meant to provide for each adult fish anyway, so, what is the problem?

The problem is, I see examples where Goldfish Keepers have far exceeded these fish per liter densities and their fish still grow large quickly.

Over the years I have done various experiments to establish what exactly is the combination of factors that do and don’t affect Goldfish growth. Here is what I have found so far.

Basic Growing Conditions

Basic growing conditions that have to be met first are:

• The fish must be in perfect health and parasite free
• Food must be high in protein, 40-50%
• Water temperatures must be high, 25^oC being the minimum
• High water quality must be maintained, along with high oxygen saturation.
• Juveniles (under a year old) grow the fastest.

Water Changes

The well-known technique of many breeders is to simply make complete water changes daily. This solves the growth inhibiting pheromone theory (Goldfish giving off a pheromone that stops the growth of other fish species, including themselves), removes waste and replaces lost minerals.

This is fine if you are not on a metered water supply, have the time, or climate change doesn’t cause water restrictions in times of drought.

Latest Experiments

Goldfish are a hard water fish species so do best in water high in minerals, magnesium and calcium for example.

I am currently running two experiments that have eliminated some of the water parameters that don’t affect the growth rate, as long as they are within an acceptable range. By way of examples these include:

• PH. Low pH affects growth rates of carp; they need a minimum of 7.0, higher is better.
• KH (Carbonate hardness). Goldfish prefer a dKH around 5-8
• GH (General hardness). Goldfish require a dGH of 7 or above.
• NO₃ (Nitrates). As long as nitrates are kept at a reasonable level (below 40ppm), I haven’t found evidence to suggest they affect growth.

Your Assistance is Required

Within the next month or two I expect my experiments to produce some conclusive results I can share with you. In the meantime, I need some information from my readers that have no trouble growing their fish large and fast.

The fish in the image above tripled their size in 12 months, in a 30 gallon aquarium, and the water was not changed daily. (I hope you don’t mind me using your image Diane).:)

Could those readers that qualify please answer these questions by reply email:

1. Is your water hard or soft?
2. How often do you do water changes, and how much?
3. Food brand/type

P.S. As this is the last e-Zine before Christmas, have a very merry festive season and I hope Santa brings you all you ask for.

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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