Temperature (part 1)

Fish are cold-blooded animals. This means they don't have a "thermostat" to maintain a constant body temperature, as mammals and birds do. Fish therefore depend on their ambient temperature for their functioning. In our case, the temperature of the pond water.

Coldwater fish

The fish we keep in our ponds are so-called "coldwater fish," meaning they can live comfortably in a temperature range between approximately 4 and 25 degrees Celsius. So-called "tropical" fish require a much more constant temperature, often fluctuating between approximately 20 and 27 degrees Celsius. Therefore, they can only be kept effectively in heated aquariums or ponds. Coldwater fish commonly kept in Dutch ponds include carp (koi), goldfish, ide, minnow, tench, and sturgeon.

Koi

Koi can be kept well in our ponds, provided we meet certain temperature requirements. Although koi have a fairly wide temperature tolerance, they are very sensitive to sudden fluctuations. Much worse than, for example, goldfish. These sharp fluctuations can occur in shallow ponds or ponds with a low volume. These ponds heat up (too) quickly and cool down (too) quickly. Temperature fluctuations in nature are much more gradual due to the large volume, meaning that carp are not evolutionarily adapted to sudden changes. When transferring fish, it's wise to take your time. By floating the bag of fish on the water for an hour or two, the temperature inside the bag will slowly adjust to the new conditions. It's best not to place koi in water that is more than three degrees higher or more than two degrees lower at once.

Food

Cold-blooded animals like fish require much less food at lower temperatures. This is because they don't need energy to maintain their body temperature. At lower temperatures, metabolism slows down and bodily functions slow down. The required food composition also changes. It's therefore advisable to provide food tailored to the season and to reduce the amount as the water cools. Below eight degrees Celsius, it's wise to stop feeding altogether (with the exception of sturgeons), as digesting food requires more energy than it provides. This isn't a bad thing; the fish use their reserves built up in the fall to survive the winter in good health. Avoid temperatures below four degrees Celsius at all times! I'll return to this later in this article.