Deciding not to run a heater in the tank does not necessarily limit you to only gold fish or bettas. There are actually many different types of fish you could keep in a cooler water environment. Some pet stores may not know the full variety and may only recommend gold fish or cloud minnows, but in reality there are many more. The key to any fish tank is stability in water chemistry, including temperature. Assuming the temperature in your house doesn’t fluctuate massive amounts throughout the day, you can run a tank with no heater. If your house temperature ranges somewhere between 65-75° F depending on the time of year, here is a list of fish that can thrive in your aquarium. Parts two and three will include which invertebrates and plants you can include in a room temperature tank.
Paradise Fish: This fish does well in an unheated tank, although can be semi-aggressive if in a smaller tank. Males are especially aggressive towards other males. Unless it’s the only fish in the tank, you should keep this in a 20 gallon tank minimum. They can be a very colorful addition to any unheated tank, and will even pair up if given the chance.
Danios (Zebra, Pearl, Leopard, Giant, etc.): Most danios do well in cooler water because it closely mimics their natural habitats. Generally, these fish are small, although there are larger varieties. Despite their small size, they are very active swimmers and do better in a larger tank. They also do best in schools and should be purchased in groups of 5 minimum. If there are other small schooling fish in your tank, the danios will school with them. So as long as you don’t buy one danio and put it in a tank by itself, they will be fine.
Killifish: Killifish are very colorful active fish. They can be a great addition to an unheated tank. They are not aggressive towards other fish, don’t let the name fool you. Males may squabble if in a smaller tank, but females will be fine together. They do best in an aquarium with live plants, although it is not necessary. Although they will eat flake food, they do especially well on live food. If you’re interested in learning how to easily culture your own live food, follow that link. They don’t need to be kept in schools, however they will school with other killifish or other small fish.
White cloud mountain minnow: This is one of the most commonly recommended fish when someone wants to keep an unheated tank, but does’t want goldfish. They are extremely hardy and easier to care for. They are very peaceful fish and can be kept in schools. In terms of tank size, they can be kept in a smaller tank and still do great. They also come in two different varieties, one is darker with red fins, while the other is more of a gold color. This is a great beginner fish or an addition to an established tank.
Guppy: Guppies are another great option for an unheated fish tank. They come in a huge variety of colors and are generally peaceful. They shouldn’t be kept with fish that nip fins though, because males tend to have longer fins. Guppies also bred very easily and are live bearers. If you have a male and female, be ready for babies. Another alternative is to just keep all females or males in the tank. Guppies even do well on their own, and don’t need to be kept in schools like other fish. They can be kept in smaller tanks and will eat any commercial fish food.
Bloodfin and Black Skirt Tetras: These are two different types of tetras that can be kept in an unheated tank. They do best when kept in schools and should be kept in a 20 gallon minimum since they are active swimmers. They don’t grow very large and are considered peaceful fish. They are both hardy fish once they are acclimated to your tank.
Gold barb and other barbs: Gold barbs are a hardy little fish that do better when kept at cooler temperatures. They are a very active fish that do best when kept in groups. If not kept in schools, they tend to be less active and shy. They are a hardy fish that won’t grow more than a few inches. They can be kept with plants, however they may nibble on them on occasion.
Peppered Cory Cat: Cory cats are one of the best scavenger fish you can get. While many only tolerate tropical water, the peppered cory cat can thrive under cooler water conditions. In fact, in an unheated aquarium, I had Peppered Cory Cats regularly breed. Cory cats are bottom dwellers and will eat the excess food that makes it to the bottom of the tank. Just make sure they are getting enough food though, don’t rely on scraps being enough for them. Cory cats do best when kept in groups. A lonely cory cat will be shy and stay hidden most of the time. When you keep them in groups, even just three, they are much more active and seem generally happier. Since they stay small (2 inches) they can be kept in smaller tanks, but do best with fine gravel or sand as a substrate.
Weather loaches: Weather Loaches do great in an unheated tank that tends to be on the cooler side. The only drawback is they tend to grow quite large (10 inches) and should be kept in a large tank. They can be very active and should be given ample space to swim. They are a bottom dweller and will even bury themselves. Because of this, you should make so you use either sand or very smooth gravel so they don’t get injured while burying themselves. This fish is extremely hardy due to its ability to breath air. When kept in lower oxygen water, instead of relying on oxygen in the water, it can breath air.
Goldfish: Goldfish are the most commonly kept fish in an unheated tank. They come from cooler waters in Asia which makes them excellent candidates for unheated tanks. Many people think of goldfish as boring orange fish, but goldfish come in a wide variety of shapes and colors. A drawback to goldfish is they are some of the messiest fish you can keep, so you will need to make sure you give them adequate filtration. Despite the myth they grow to the size of the tank, gold fish can grow large and should be kept in a larger tank. One last thing to mention is, if kept with plants, gold fish will eat them.
Betta: You may be thinking, Betta’s should be on this list. While a Betta may be able to survive in an unheated fish bowl, they won’t thrive. Bettas are considered easy beginner fish because they tolerate the harshest conditions. Just because they can tolerate living in a bowl, doesn’t mean they have to live a life of solitude in a bowl. Bettas are actually peaceful fish, despite being nicknamed Chinese Fighting Fish. While they will fight to the death other bettas, to many other fish they are completely peaceful provided they don’t look like bettas. The real problem with keeping bettas with other fish isn’t the betta killing them, but the other fish killing the betta. The long flowing fins of the betta aren’t just attractive to people, other fish that nip fins love them as well. If you plan to keep a betta in an aquarium with other fish, you will need to be sure to chose fish carefully. Also, they aren’t very strong swimmers so they need lower flow tanks.
There are other fish that can live in an unheated tank, however the above list provides a pretty good variety to build a great tank. If you decide you want to keep live plants and invertebrates in your unheated tank, I’ll be covering which ones will survive and thrive in an unheated environment in upcoming articles.
All images provided by Wikimedia Commons