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The Goldfish Gazette, Issue #139 Water Temperatures July 30, 2025 |
Goldfish Care TipsA Free Monthly Resource For Goldfish Enthusiasts In This Issue Goldfish are poikilothermic, meaning their body temperature closely matches the surrounding water temperature. Water Temperatures
Goldfish Natural Habitat Ambient TemperaturesWe know Goldfish can live in a wide range of water temperatures, but why is this, and the question often raised is what temperature should I keep my Goldfish at?If we examine the area in China that forms the natural range of the Prussian or Gibel Carp, the ancestor of the Goldfish, and consider the range of ambient temperatures in a centrally located city, such as Wuhan, the seasonal temperature range is high. The average temperature in January (winter) is between 0 and 8oC, and the hottest month is July, with temperatures between 26 and 33oC. The seasonal temperatures experienced by the carp are significantly higher compared to most tropical fish species. Seasonal Temperature ChangesSo, we now know why Goldfish can live in extremes of water temperatures, their natural environment experiences significant seasonal differences. But how does that affect their natural behavior?Winter –
December–February Spring – March–May Summer – June–August Autumn – September–November Seasonal Feeding ChangesIf we have outdoor fish ponds, our feeding regime needs to follow the seasons.Fish often survive the winter, but then die in early spring because they didn't build enough fat reserves in the autumn due to underfeeding. Although seasonal temperature differences won't be as significant as those for outdoor ponds, the feeding regime for fish kept indoors follows the same guidelines as for outside ponds, unless a heater is installed. As a general rule, the warmer the water, the more interested the fish are in food. At 12oC, my fish feed, but take a while to get through the food. At 25oC, they are practically leaping out of the water at feeding time and food disappears quickly. This behavior shows the importance of feeding based on water temperature. Water Heater or Not?Many Goldfish keepers heat their fancy varieties, some as high as 27/28oC (81/82oF).They reason that their fish appear more robust, active, and less inclined to swim bladder (buoyancy) issues. Personally, I think this is unnecessarily hot, and water at this temperature is low in dissolved oxygen, maintaining high water quality is extremely important, and the metabolism of the fish is constantly high (shortened lifespan). I generally don't use heaters for adults, and I keep Celestials, Water Bubble Eyes, and Black Moor inside and outside, regardless of the season. I do live in a temperate climate, but my pond water is presently dropping to 5oC during frosty mornings. The inside temperatures are around 9oC. I use heaters if I have had a late spawning, and the juveniles haven't reached a reasonable size before the cooler autumn temperatures set in. Still, I keep the temperatures around 23-25oC, finding higher temperatures than this don't make the fish grow any faster. Thai Sourced GoldfishIf I kept Thai-sourced fish, I wouldn't let them experience winter temperatures, as they have been raised in very hot water for many generations. I would use a heater set at the minimum of around 20oC.ConclusionSo, to answer the question of what temperature to keep Goldfish at requires three answers:1. Let the ambient temperature dictate their water temperature, but feedings need to reflect that. 2. Heat your fish year-round, but this will shorten their lifespan, and they won't experience the natural seasonal temperature differences used to trigger activities such as spawning. 3. If you own Thai-sourced fish, heat them so water temperatures don't drop below 20oC. 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. www.facebook.com/aboutgoldfish |
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