Warm Water vs. Cold Water Fish

What's the difference between warm water fish and cold water fish? This is one of the first things an aquarist has to learn about. Don't worry, it's easy!

Warmwater Fish

Warm water fish, aka tropical fish, generally thrive in water that is between 72 and 80 degrees Fahrenheit. Some fish prefer it at the lower end and some prefer it even higher than 80 degrees, so the exact temperature you use might depend on the specific species you have in your fish tank. It's popular to use 78 degrees because most tropical fish across the board can survive just fine in that.

Coldwater Fish

Cold water fish prefer water that is between 65 and 70 degrees Fahrenheit. The best-known for loving coldwater aquariums are goldfish, pond fish and koi.

Both-Water Fish?

There are some aquarium fish, such as corydoras (corys), loaches, danios, and angelfish, that are considered to be “warmwater fish” but are comfortable in cooler waters and warmer waters alike. Most people keep them in warmwater aquariums.

Lumping fish into 2 categories (warm and cold) oversimplifies everything a bit but it saves us from having to memorize the preferred temperatures for every species.

Obviously, it's best to try to put fish together that prefer an optimum temperature that is within a few degrees of each other, but not everyone wants to get that involved in the process. Simply knowing whether your fish is warm or coldwater and knowing the temperature range for each is often all you need... along with a fish tank thermometer!