Goldfish Care Tips

A Free Monthly Resource For Goldfish Enthusiasts
June 2025
Issue #138

In This Issue
Maintaining Feeding Levels

Fast-growing Goldfish can quickly out-grow the amount of food you think is adequate.
A single-tailed Goldfish variety doubles its weight with every 25% increase in length, every 20% increase for deep body varieties.

Maintaining Feeding Levels

A mix of Repashy and pellet foods ready to feed out

I recently encountered this problem while feeding a group of young Black Moor for a growth experiment. I noticed they weren’t growing as fast as I expected.

After weighing the fish, I found I was feeding them at 2% of their body weight per day, not 3% as I thought.

Feeding by Weight

As I have mentioned before, Goldfish should be fed between 0.50 and 3% of their body weight daily, depending on water temperature. Feeding above 3% is pointless as they don’t process the food efficiently.

To show how much weight increases as Goldfish grow, listed below are the weights of a young Moor over 3-months, showing the dramatic increase in weight at each 10 mm (3/8") increase in length.

50mm 8.5g
60mm 17.5g
70mm 28.5g
80mm 45g
90mm 68g

So, feeding an 80mm Goldfish weighing 45 grams at 3% of its body weight per day, that works out to 1.35g of dry food daily.

But this fish grew 10mm in three weeks. It now weighs 68g, a 51% increase in weight, so now it should be fed 2.04g per day. Feeding 1.35g per day is only 2% of its body weight, so the fish will slow down growth from now on and get progressively slower if feeding isn’t increased.

Gel Foods

There is a danger with gel foods in that they have a high water content. For Repashy foods mixed at one part food mix to three parts water, that is 85%.

This means if you feed a 68-gram fish dry prepared food at 3% body weight per day, the amount of food required is 2.04 grams (68g x 0.03). However, if you are feeding a gel food, you need to feed 13.6 grams (2.04g/0.15) to achieve the same feeding level.

Temperature Based Feeding

I use five key temperature ranges when feeding my adults.

1. 10^oC and under, I don’t feed them.
2. 11^oC to 14^oC, I feed at 0.50% body weight per day
3. 15^oC to 19^oC, I feed at 1% body weight per day
4. 20^oC and above 2% body weight per day
5. 25^oC and above 3% body weight per day for fish I want to achieve fast growth.

For amounts above 1%, the feedings need to be spread over three feedings or more, as it takes a while even then for the fish to consume that amount of food.

I feed 50% Repashy (dry weight equivalent) and 50% pellets split over three feeds, and at 3%, my fish take about 10-12 minutes to get through the food.

For my adults that are big enough, I feed at 2% split over three feeds during the growing season when temperatures are above 20^oC.

I would limit feeding to no more than 1% per day for those who do not want their fish to quickly out-grow their aquarium. The fish will still grow but much slower than if fed at 3%.

Conclusions

If you have juvenile fish you want to grow quickly, or even undersized adults, you need to check their weight frequently. At 25^oC and above, I weigh my fish weekly.

Don’t over-feed your fish. 3% body weight per day is a large amount of food, and the most Goldfish can process efficiently. This amount should only be fed to juveniles and undersized adults.

Don’t under-feed your fish. Gel foods are mostly water, so they are only equivalent to 15% of the same weight of dry food.

I use jewelers’ scales to weigh out food portions for each of my ponds and aquariums as each holds different numbers and sizes of fish.

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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