An aquarium water heater is an essential item for many fishkeepers, especially if you live in a cool or temperate climate far from the tropical heat of the equator. However, a few special fish species can thrive in cooler conditions, and many of them are comfortable in average indoor temperatures.
Read along to learn about five freshwater fish that you can keep without a heater.
Why Do Most Fish Need Heaters?
The fish species we keep in our home aquariums come from diverse habitats and countries across the globe. Most are at home near the equator in the tropical waters of Southeast Asia, South America, and Central Africa, where temperatures stay warm throughout the year.
Fishkeepers who live in these tropical latitudes can often keep these fish without altering the water temperature. However, those of us living in cooler climates rely on aquarium heaters to keep our pets warm and comfortable. Installing a water heater in your fish tank is often a critical step because incorrect temperatures are one of the major reasons why pet fish die.
Whether or not your fish will need a heater depends on many factors. The most important variables are the average temperatures in your home and the needs of your specific fish species. Learn why temperature regulation is so important and discover if you will need a heater for your tank.
Fortunately, there are a few special fish out there that don’t need a heater when kept in average home temperatures between about 68 and 72 degrees Fahrenheit. Read on to learn about five species that are suitable for an unheated aquarium.
1. Celestial Pearl Danio
The celestial pearl danio (Danio margaritatus) has become extremely popular for its beautiful colors and patterns. These tiny fish from Southeast Asia are ideal for smaller aquariums with live plants and other small, peaceful tankmates.
Also known as the galaxy rasbora, the celestial pearl danio grows to less than an inch in length and can be kept in a tank as small as 10 gallons. They are pretty shy little fish, so choose tank mates that won’t bully them or outcompete them at meal times.
Celestial pearl danios thrive in cooler water than most tropical fish, and many aquarists are able to keep them without a heater. However, these fish will not survive very cold conditions, so they are only suitable for unheated tanks that stay above the mid-60s Fahrenheit in winter.
Celestial Pearl Danio Care Requirements:
- Temperature: Lower 70s Fahrenheit
- Tank size: 10 gallons
- Recommended pH: 6.5-7.5
2. Japanese Ricefish
The Japanese rice fish (Oryzias latipes) is another miniature species that prefers cooler conditions. These fish are a popular choice for small outdoor ponds, although they also make great aquarium fish for small tanks.
Traditionally known as Medaka, the Japanese rice fish is a species with understated beauty. However, they have been bred into many different forms with various body shapes, fin types, body colors, and eye colors.
Japanese ricefish tolerate a wide range of temperatures and will thrive in homes that remain warmer than 60 degrees Fahrenheit in the winter.
Japanese Ricefish Care Requirements:
- Temperature: Low 60s to mid 70s Fahrenheit
- Tank size: 10 gallons
- Recommended pH: 7-8
3. Zebra Danio
The zebra danio (Danio rerio) is a popular and affordable aquarium fish that comes in many patterns and colors. The wild-type fish has dark horizontal stripes, but aquarists have also produced an interesting spotted pattern (called the leopard danio) and even fish with long, flowing fins.
These low-maintenance aquarium fish have also been genetically modified to show off some extremely bright shades. Glofish danios are available in many interesting colors, including green, red, and blue.
The zebra danio is a small but active fish that grows to about two inches long. These fish do best in a fairly large aquarium (20+ gallons), and they are very tolerant of low temperatures. Zebra danios can be kept without a heater if their water stays above the low 60s Fahrenheit.
Zebra Danio Care Requirements:
- Temperature: Mid 60s to mid 70s Fahrenheit
- Tank size: 15+ gallons
- Recommended pH: 6-8
4. Weather Loach
The weather loach (Misgurnus anguillicaudatus) is a bottom-dwelling fish with an interesting behavior. These unique creatures are said to become highly active just before a storm because they can sense changing air pressure.
Weather loaches (also known as dojo loaches) are fairly large fish, so adults will need a tank that holds 55 gallons or more. They are very peaceful fish despite their size, although they could be a problem for shrimp or very small and slow-moving fish.
Weather loaches will do well in aquariums that remain in the mid-60s Fahrenheit in the coldest months. Summer temperatures should not exceed the mid-70s.
Weather Loach Care Requirements:
- Temperature: Mid 60s to lower 70s Fahrenheit
- Tank size: 55+ gallons
- Recommended pH: 6-8
5. Goldfish
Many fishkeepers add goldfish to their tropical aquarium, but goldfish actually prefer cooler water. These surprisingly intelligent fish are at home in the cool waters of East Asia and are hardy enough to thrive outdoors all year round in many parts of the world.
Goldfish also make great aquarium pets, although it’s important to provide enough space for their adult size. The smaller fancy breeds are better suited to indoor aquariums and they don’t need a heater in average home conditions.
Goldfish Care Requirements:
- Temperature: Upper 60s to lower 70s Fahrenheit
- Tank size: 20+ gallons (depending on breed)
- Recommended pH: 7-8
