Goldfish Care Tips

A Free Monthly Resource For Goldfish Enthusiasts
February 2025
Issue #134

In This Issue
Overfeeding Goldfish

The warnings printed on food containers not to overfeed Goldfish are to ensure all food is consumed before it dissolves into a cloud of inedible dust that pollutes the water, not the danger of actually overfeeding your fish.
But is it possible to feed our Goldfish more food than they can efficiently process?

Overfeeding Goldfish

Weighing Celestial on Jeweler's scale

Yes, I can hear you now; "but you constantly tell us you can't overfeed Goldfish!"

I still stand by that claim. Let me explain.

My claim is that if you feed your Goldfish a food that dissolves slowly, such as a gel food, your Goldfish will eventually consume that food no matter how much food is fed, be it 1-3% or 10-15% of its body weight per day.

I know this because that is precisely what I have been doing during some testing.

I feed my adult fish 2% of their body weight per day over two feedings during the growing season, and after many decades of Goldfish keeping, it feels about right. So, I started to think, are the fish being fed 10% of their body weight per day in my testing, processing all that extra food?

The difference between 3% and 10% of body weight is huge, and they didn't appear to be growing any faster than fish fed 2% of their body weight/day.

Scientific Study

During the testing I have been doing, I came across a scientific study done with common carp (Cyprinus carpio) by the University of Galati in Romania.

The test was to establish the ideal feeding level for the growth performance of common carp.

The research was important because common carp are a significant food source in many countries, and food is a major cost.

The test comprised of 4 feeding levels, 3%, 4%, 5%, and 6% of body weight per day over three feedings for 31 days, fed to carp weighing on average 11 grams.

The results were surprising. Note that the testers were more interested in weight gains than final body length as these are food fish.

From an initial body weight of 11g, the average weight gained over the month for each feeding regime was:

3% 10.34g
4% 7.83g
5% 7.77g
6% 7.66%

We know a long-bodied Goldfish variety (Common, Comet) doubles its body weight when it increases in length by 25%, so, in a month, the different feeding tests grew in body length by 24.3%, 21.5%, 21.4%, and 21.3% respectively, so, the more they were fed, the less they grew!

Unscientific Testing

We know Goldfish are from the same carp family, so I assumed my test results would be near enough to the common carp. I am more interested in body length gain than body weight gain.

I was doing a growth test with two tanks of two-year-old Celestials and feeding 10% body weight/day.

I continued this for one tank but I dropped the feeding down to 3% body weight/day with the other.

After a week, I measured control fish from each tank. Both control fish had grown 3mm.

I am continuing my testing feeding at 3% body weight/day.

The advantages of not feeding food that the fish aren't going to process efficiently are many and obvious:

1. Significantly lower food cost
2. Fewer water changes
3. Less filtration needed (less bio-load)
4. Healthier fish

Conclusion

We can overfeed our Goldfish because they will eat everything we provide. Feeding more than about 3% of their body weight daily is only costing us unnecessary expense, making work for ourselves and creating unhealthy fish.

Feeding can be much higher for juvenile fish (under 12 months old) because they are in their fastest-growing phase, and food is only used for metabolism and growth.

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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