Autor: Dr Sabine Özgönül-Wagner
Time and again, you find yourself at a pond where you unfortunately realise that there is very little water between the individual fish. Very often, koi enthusiasm creeps in slowly. You have a small garden pond and receive a small koi as a gift from friends or family. Over time there are more and - oh wonder - the fish grow. This often works well for years, even with a small filter, until suddenly the point is reached where the pond is simply too full and, in the worst case, the fish start to die. The question therefore arises: How many koi should I keep in the pond?
But how much space does a koi need?
How many koi per litre? This depends on various factors. Not least, on the existing filter technology. Let's assume a pond that is properly filtered and aerated, in which regular partial water changes are carried out and which is not fed too much. Then, as a rule of thumb, we can assume 1 to 3 m3 per koi, depending on the size of the fish. A koi of 40 cm (corresponds to approx. 1 kg body weight) requires approx. 1 m3 and the larger the fish, the more water volume it needs.
It's not just about the fact that the water is difficult to keep clean when overstocked, but also about the well-being of the fish. We humans also need a "comfort distance" to our fellow human beings (this varies depending on how much we like the person in question) and feel uncomfortable or even stressed if this distance is constantly not maintained. This also causes social stress in the animals, which in the worst case leads to an impairment of the immune system. This, in combination with the very difficult hygienic situation with massive overstocking, makes it easier for parasites and bacteria to multiply rapidly and leads to constantly sick fish.
Do not fill a new pond to capacity straight away
Therefore, always plan pond construction well and don't get carried away with spontaneous autumn sales at the koi dealer. A pond does not have to - and should not - be fully stocked in the first year. Take your time and consider whether there is enough space in your pond before making any purchase. Above all, bear in mind at all times that the fish will grow. Remember: depending on the variety, a koi can grow up to 120 cm and weigh over 20 kg.
