Myths about Goldfish and their care
MYTHS OF GOLDFISH AND THEIR CARE:
“Goldfish are coldwater”
This isn’t completely a myth, goldfish are definitely well adapted to cold water. They can live in water down to the freezing point, as long as it stays liquid. The myth part of this is that they can only be in cold water. This is not true. They are actually eurythermal, which means they can thrive in a wide range of temperatures. Fishbase.org has their temperature range listed as 0-41C (32-105.8F). (1)
It is important to distinguish between truly coldwater fish and those who can thrive in warmer temperatures. Truly coldwater fish are species that cannot thrive in warmer temperatures. The increased temperature causes stress, failure to thrive, and can kill them. This would include species like trout and white cloud mountain minnows. These are species that when in higher temperatures show signs of stress such as reduced coloration, overall failure to thrive, and more extremes such as severe stress, illness, and death. This is not the case with goldfish. This is not a case of goldfish simply tolerating higher temperatures then they are given credit for, they thrive in these temperatures just as well as they do in lower temperatures. In higher temperatures they do not show these signs of stress and failure to thrive. They can thrive in higher temperatures.
The countries the goldfish is native to are: China, Hong Kong, Japan, Laos, Macau, and Myanmar. The countries the goldfish has been introduced to and is now naturalized in (maintaining populations) are very numerous, but include: Afghanistan, Argentina, Australia, Bolivia, Brazil, Chile, Colombia, Costa Rica, Ethiopia, India, Indonesia, Iran, Iraq, Korea, Madagascar, Malaysia, Mexico, Peru, Philippines, Puerto Rico, Samoa, Saudi Arabia, Singapore, South Africa, Thailand, Uruguay, U.S. Virgin Islands, U.S.A. (including Florida and Hawaii), Vietnam, and Zimbabwe. (2)
The following map shows the natural and introduced distribution of goldfish in the wild. The blue areas are where they are found naturally. The red is where they have been introduced and established populations.
The CIA World Factbook lists China as varying from sub-arctic in the North, to Tropical in the South.(4) Their natural range includes the Tropical Southern region as well as Hong Kong and Macau. The same source lists Laos as having a Tropical climate.(4) You can see how Tropical of a climate their natural range reaches, less than 15 degrees from the equator in Myanmar, Thailand, and Laos.
There are some significant implications in the range included in the introduced range of the goldfish. Throughout Indonesia and Malaysia it sits right on the equator. It also stretches continuously from India through the Middle East and into Saudi Arabia. Africa also shows their distribution within 30 degrees latitude. One of the most significant introduced areas is South America. Almost all of South America is now the introduced home of this supposedly coldwater species. This is not only significant in terms of latitude and temperature, but these are the exact same waters so many of the hobby’s tropical fish come from. Goldfish in the wild are literally swimming alongside the exact species kept in tropical tanks, and yet it is claimed to be too hot for them. In addition to all of this is their distribution in Mexico and into the United States. In the U.S. they are not limited to temperate Northern regions, but are present in tropical areas such as Hawaii and Florida. They are not just in large bodies of water that will have a relatively stable temperature throughout the year and day, but they thrive in small ponds that will quickly rise in temperature under the hot summer sun in Florida.
These are not the coldwater fish we have thought of them as. Beginner books list them as coldwater and frequently give temperature ranges to match this. So it is no wonder people think of them as coldwater fish, we are told they are from the very beginning. But the evidence simply doesn’t support this.
There is even some indication of higher temperature being beneficial in multiple ways. It has been shown that pigmentation is increased with higher temperature. One study found that the ideal temperature for pigmentation was 26-30C (78.9-86F). (5) Pigmentation (coloration) is generally considered one indication of overall health and ability to thrive. In a different experiment it was found that the highest growth rate was at 28C (82.4F). (6) In both of these studies the ideal temperatures were found to be the highest temperatures used in the experiment. Since they did not use even higher temperatures it is unknown based on these experiments if even higher temperatures would have produced even better results.
Numerous goldfish keepers have found that higher temperatures do not have negative effects on goldfish, some even cite their goldfish thriving in temperatures as high as 90F. Many of the fancy varieties are bred in tropical climates such as Hong Kong and Thailand. Some keepers have even noted significant stress in these fish when moved immediately in to cooler temperatures upon being imported. It is recommended that fish bred in warmer regions are kept in higher temperatures, at least for a an extended period, at least a few weeks, when they are first imported to reduce the stress of moving from a warmer to cooler climate.
Author’s experience and conclusion:
I have had goldfish in the same tank as discus and other tropical fish. I use them to help control the duckweed and crystalwort that I now regret introducing one of my tanks. These are the same goldfish I usually keep in the room temperature goldfish tank. I see no signs of any issues while they are in the tropical tank. They are just as active, if not a little more active. They are just as colorful. They eat just as well. I have seen no signs of any problems with keeping them in this temperature. I have talked with many other goldfish keepers who have or have had goldfish in tropical temperatures. From ponds in tropical areas like Florida and Thailand, to having them in tropical tanks in general.
But what does this mean for the hobby of keeping goldfish? We do not need to go buy heaters for our goldfish tanks. They thrive in room as well as tropical temperatures. What this means is that when people ask what they can keep with goldfish, we need to focus on the real problems with goldfish in the same tank as other fish and not just regurgitating the myth of temperature problems. This does not mean we can just start putting goldfish in tropical tanks. Goldfish are not compatible with most tropical fish. Almost all are too aggressive, too nippy, or too small to be in with goldfish.
1 Fishbase.org Carassius auratus
2 Fishbase.org Countries of Carassius auratus
3 World Map in black and white (color added by author)
4 CIA The World Factbook
5 Aquaculture Nutrition, 2005, 11 p19-23, “Effect of microalgal biomass concentration and temperature on ornamental goldfish (Carassius auratus) skin pigmentation”. L. Gouveia, and P. Rema.
6 Aquaculture, 1995, 136 p341-349, “Influence on feed supply, temperature and body size on the growth of goldfish Carassius auratus larvae. P. Kestemont
Last edited by Fishguy2727; 11-13-2008 at 01:14 AM.
Aquarist since 1995
Biologist and Published Author in Multiple Aquarium Magazines
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