Is Water that’s Too Warm Dangerous for Fish?

With climate change creating more extreme weather conditions, unfortunate phenomena such as massive fish die-offs are becoming more common. A 2019 study conducted by marine biologists from the University of California and Reed College estimates that fish kill events caused by heat waves will double by the year 2050 in some Wisconsin lakes.

Water temperature plays a very important factor in the health of many aquatic species, particularly those that aren’t migratory since they’re not instinctively predisposed to swim away in search of cooler water. In an enclosed ecosystem such as a saltwater or freshwater aquarium, fish keepers are responsible for regulating the water temperature, and they should know that very warm water can be harmful to certain species.

Water Temperature and Biochemistry

The practice of regulating water temperatures in an aquarium comes down to providing adequate oxygenation for all species. Naturally, boiling water will kill all species, but temperature management is all about providing adequate levels of dissolved oxygen. As water temperature rises, fish have fewer O2 molecules to breathe. Heat evaporates water as well as oxygen particles. There’s also the matter of fish becoming more active during warmer seasons, which translates into a higher metabolism and the need for more oxygen.

Fish Cannot Regulate Body Temperature

Unlike felines and other terrestrial species, fish are cold-blooded creatures that cannot regulate their internal temperature. It should be noted that tropical fish, both freshwater and saltwater species, can withstand a range of water temperatures, and this is part of their resiliency. When a thermostat is programmed to keep temperatures between 75 and 80 degrees Fahrenheit, the hardiest freshwater species will be happy.

When High Water Temperatures Get Dangerous

When the tank thermometer registers 85 degrees Fahrenheit, conditions are still manageable for the hardiest species because they’ll seek the cooler bottom and wait for temperatures to fall, typically at night. Things become worse once the water temperature reaches 90 degrees and stays at that level for several hours. At this point, you should make sure the heater isn’t stuck in the “on” position, shade the tank from direct sunlight, turn off the aquarium lights, and put a securely fastened fan over the top of the aquarium. Another problem related to high water temperatures is that the bioload will increase and algae bloom could set in, so you may need to do more cleaning and water changes.

Cold Water Aquarium Species

Some species of fish thrive in cooler aquarium water. For example, Clown Killifish are a friendly and low-maintenance species that thrive in temperatures under the 75-degree threshold for tropical fish. Pearl danios are very resilient and enjoy swimming around plants. Chinese loaches will help you keep the tank free of algae and detritus. Most aquarium catfish that stay close to the substrate won’t need a heated tank.

Whether you need a heating or cooling system or any other essential supply for your aquarium, you can find what you’re looking for at Aquatic Warehouse. We’re located in Kearny Mesa, or you can order what you need from our website. If you have any questions, don’t hesitate to call one of our friendly and knowledgeable representatives at 858-467-9297.