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Which Fish Can I Keep In My Cold Water Tank? Tropical or Cold Water Fish?The first decision to make is whether you want to keep fish which require a heater in the tank, or not. Most tropical fish must be kept in temperatures ranging from 25° to 27°C, although a few species require their environment to be slightly warmer or cooler than this. Cold water fish are happy at normal room temperature for most homes, being quite comfortable at 15°C. No matter which you choose, it is important to have a thermometer attached to the tank, in order to monitor extreme water temperature changes, whether this is caused by a fluctuation in the environmental temperatures, or a heater malfunction.  True Cold Water Fish Throughout our information, we refer to fish who don't require a heater in their tank to thrive as 'cold water fish'. However, this is not strictly the case, and temperate fish tends to be a more appropriate description. True cold water fish would require a chiller in their tank, which would cost a lot more to buy and run than a heater. There are strong restrictions on true cold water fish being brought into the UK, due to their ability to survive in our rivers and predate upon native species. From here on in, though, we will describe our temperate, home loving, fish friends, as cold water fish, as that is what many of us have always known them as. Cold Water Fish Common Goldfish & Varients A variety of fish which will happily live in a tank without a heater are readily available. The Common Goldfish and its many varieties, such as the Shubunkin and the Comet, have an elongated flattened football shape, and tend to be a hardy species to keep. They can live in water with temperatures ranging from 12-26°C, with a pH of 6-8, which is very similar to tap water. The common goldfish doesn’t require a heater and needs only minimal care if living in a well filtered aquarium of 20-30 litres.  Fancy Goldfish The fancy goldfish has an egg shaped body and encompasses many varieties such as the Oranda, Ranchu, Ryukin and Black Moor. Care should be taken with the species which have protruding eyes, as they tend to have poor vision so the faster species will outcompete them at feeding time. The species with protruding eyes can also be more prone to injury and therefore infection, so should only be kept with other slow moving, delicate species. Although fancy goldfish do not require a heater in their tank, many are not suitable for keeping outdoors as they do require an environmental temperature of no less than 13°C.  Minnow & Danio The White Cloud Mountain Minnow is one of the most popular small cold water species available, and for good reason. They have a typical lifespan of 5+ years, are a schooling species so are enjoyable to watch, and enjoy water temperatures of 18-22°C. The Zebra Danio is another popular species, a fish who also enjoys schooling with his tank mates. Due to the small size of these two fish types, reaching adult lengths of only 4cm, they are ideal for smaller, filtered aquaria.  Barbs Rosy Barbs, Golden Barbs and Odessa Barbs can all be kept successfully in tanks without a heater, thriving in water temperatures between 18-22°C. These are shoaling species and should be kept in groups of 5 or more. They enjoy stand-offs amongst friends, and create an personality filled and enjoyable aqaurium to watch. They can be nippy so should never be kept with Common or Fancy Goldfish, but will do well in tanks with other cold water barbs, and groups of minnow/danio.  Peppered Corydoras Unlike most other Corydoras, the Peppered Cory prefers lower temperatures of 18-25°C and will therefore thrive in most unheated, indoor aquariums. This hardy little fish loves company of its own species, and is best kept in groups of 4-5 other Peppered Corys. If buying from a tropical aquarium, careful attention must be paid to slowly introducing this fish to the cooler temperature of your unheated tank, over a 12 hour period.  Weather Loach A variety of loach species will do well in an unheated tank, particularly the Weather Loach which thrives in temperatures from 15-25°C. Although not a flamboyant or colourful fish, the Weather Loach which can grow to an impressive 10 inches in length, is a peaceful and hardy fish. The wonderful characteristics of the Weather Loach include their ability to survive for several hours outside of water (so all may not be lost if he escapes from the tank - well fitting lids are a must!) and to predict storms with their body movements.  Guppies, Mollies & Platies These fish are a true example of hardiness not being as it used to be. Whilst they may have survived in unheated aquaria in years gone by, these fish are rarely as hardy as they once were, perhaps due to breeding specifically for bright colours, and the lessening amount of wild caught specimens in the trade due to their ease of breeding in captivity. For this reason, we do not recommend keeping these species in a tank without a heater.  Siamese Fighting Fish aka Betta Sadly, these beautiful fish are often marketed as a fish suited to living a sad and lonely existence in a small, unheated bowl. In the wild, these fish live in warm rice paddies, with high oxygen and warm, stable temperatures, and low water circulation. The responsible Betta owner will do their best to replicate this environment, providing stable temperatures of 24-26°C. Keeping Siamese Fighting Fish without a heater will lead to a letharic fish with a low immune system. For this reason, we do not recommend keeping a Betta fish without a heater, and we suggest a heated, filtered tank of at least 15l, with appropriate tankmates. |