Winter: what must be brought in at all costs?

The low temperatures are coming, after a rather mild autumn.

Of course, the tropical fish that had been taken out to the garden for the summer have been brought back inside to warmth since October, depending on the regions.

 
You found them more colorful, more beautiful, more vibrant, and even wild again! Sometimes, you also found them more numerous.

Some less sensitive species will spend the winter outside, such as goldfish or the famous Tanichthys for example, or even others in favorable regions.

 

But the cold is coming and the question arises for plants and invertebrates.

 
"I personally spent the winter outside in the Paris region with Néocaridina davidi shrimp, which came out looking superb. A buried tank keeps the water at a more temperate temperature at the bottom, allowing many species to not suffer too much from the cold."

 

The water lice love the cold and can stay outside all winter, even running under the ice. They will be even more prolific in the spring, as they prefer frost to heat waves.

Ostracods and the Blackworm will enter a certain lethargy, waiting in the mud at the bottom for the return of spring.

 
Similarly, the daphnia will become less numerous, with only a few rare individuals surviving under the ice. In spring, the population will rebound from these survivors, but also from the floating eggs laid in the autumn, capable of surviving everything for a very long time!

It is therefore wise to bring back some daphnia at 18 or 20°C if you want to continue multiplying them for your fish during the winter months.

 

Plants, on the other hand, are quite surprising. There are those that pretend to die: water lentils and large water lentils, azolla and a few others completely disappear from the surface, surviving at the bottom of the water in a dormant form. This is how you will see them reappear in spring, as if by magic. Azolla does even better: it sends dormant forms from the bottom, while often maintaining itself at the surface as well.

The three-lobed duckweed takes advantage of the disappearance of its competitors to form beautiful green cushions on the surface, insensitive to frost.

 
Others, like the Salvinias or the floating frogbit really cannot withstand winter and will die permanently after severe frosts. If you don't bring a few specimens indoors to keep warm, you will lose them!

 

The irises, the water mint or the Purple loosestrife are not afraid of winter. They will regrow from their roots as soon as the nice days arrive, each year a little stronger. The water mint even takes advantage of winter to spread, its creeping stems resisting everything.

 

More surprisingly: the Sagittaria subulata and the Vallisneria, known not to withstand the cold, survive in my pond every winter at the bottom of the water, under the ice layer. Their leaves are shorter to avoid the surface ice, but they do not seem to suffer from the cold at the bottom of the water and multiply over the years and seasons. This behavior, completely contrary to what aquarium manuals say, is nonetheless consistent according to my observations.

Finally, the Ceratophyllum and the Water milfoil, or even the Najas (which is more surprising), spend the winter in a poubellarium or in a pond without a hitch. It's just that the Cerato changes appearance (shorter and denser strands) and that the Najas becomes a little more brown-red.

Climate change, which makes milder winters more frequent, will likely only exacerbate these phenomena of resistance in species once deemed too sensitive to spend the winter outdoors.

But bringing them into an aquarium in winter, if you prefer this option, allows them to continue to grow and green all winter, while waiting for the return of the nice days.