A pond without fish does not look like a real pond … but not all fish are suitable to live in a pond, they must be fish capable of adapting to living in cold water and withstanding the typical climatic changes outside , pond fish are usually fish of cold water.
Until recently, the most common fish in ponds were Koi carp, but currently there is a ban on their possession, transport and marketing.
I find it really curious, because recently I have been visiting a national monument and I have been able to see how in ponds «that are property of the State», Koi carp are kept … the contradictions of the legislators.
The important thing is that you know thatsome species of fish considered invasive, cannot be had, transported or bought. Another thing is that it is done or not.
Pond features
In theory any pond can be used to keep fish outside (as long as they are cold water), but in practice it is better if the pond has adequate measures.
The most important is depth. A fish pond should be at least 80 centimeters deep , so that the fish find shelter at times of maximum heat and cold.
If the surface of the pond freezes, at that depth they will have a temperature that allows them to hibernate without problems.
The same happens in very hot moments, the water temperature at 80 centimeters will be several degrees lower than at the surface.
Another detail to consider is the number of fish that we can have in the pond. As a rule, for every 10 centimeters of fish length, we will allocate about 50 liters of water.
Fish species for pond
Over time I have been describing a good number of cold water fish species, which can be kept in a pond without any problem.
Most of them can live together and share space without any problem, but it may be the case that some are not compatible … more than anything because they can be carnivores and eat others, as is the case of the Percasol … although like Koi carp They cannot be marketed, it is possible to find them in our rivers… and they are fished.
Pond fish, alternative to Koi carp
It is a pity that they do not allow marketing with Koi carp. Despite the fact that various associations are trying to have the ban lifted, at the moment this has not happened … they are still banned.
If we do not want to have problems, we have to look for valid alternatives that can also live in the pond without any problem.
Goldfish or goldfish
Goldfish are a great alternative to Koi carp, since we can find a great variety of fish with different colors and shapes, the product of a prolonged selection over time and the crossing of different species.
They are very peaceful and long-lived fish. They can live for several years in an outdoor pond without any problem. 
In order for them to remain in good condition, we must introduce a small school, since they are very sociable fish that need contact with their congeners.
Adult specimens can measure up to 20 centimeters.
Golden barbel
The Golden Barbel is a small cyprinid, between 5 to 7 centimeters in length, which is quite long-lived, it can live up to 7 years.
It is not as resistant to low temperatures as Koi or Goldfish carp, so if the frosts are strong in our area, we must move them to an indoor aquarium during the winter, safe from frost.
