At the beginning of winter the water temperature of the Aquaponics setups is dropping. Being “cold blood animals” the fish activity is decreasing to almost stop during the coldest months (depending on the fish species and temperature range). If the water temperature reaches the lowest range of your fish preferendum then they will stop eating and will simply survive on their reserves. If this period is short it’s not a problem but if the period last for a while, the fish will consume their energy reserves and once used they will become weaker and more likely to get fish disease. The key to avoid this to happen is to avoid fish stress. Any action around or in the fish tank can have an impact on your fish stress level. Most fish species are still wild animals and in case of danger their natural instinct is to swim away from the assumed source of danger. In a fish tank they have nowhere to go and in case of noise or other disturbance the fish will be trapped and stress. Their heart pulse will increase and they will fill consume a large quantity of energy for nothing. The 2 first things to do in winter in order to avoid disease opportunity are to:
Insulate your fish tank (if possible) and try to maintain a descent temperature adapted to the species of fish you are keeping
Avoid to stress the fish, don’t fish them during winter, avoid noises around the tank and give them some pipes/roots or any other element to hide underneath.
Now in order to minimise the fish energy consumption we can work on reducing the osmosis power. The osmosis is a phenomenon that pushes the water from the solution the less concentrated to the solution the most concentrated. In short the water tries to dilute the minerals. The freshwater that we use to fill our aquaponics fish tanks generally doesn’t contain much salt and therefore the salt concentration is close to 0g/litre of water. The body of the fish is working thanks to several biological and chemical mechanisms known by the name of Kreps cycle. Phosphorus and Sodium are very important minerals of the Kreps cycle, this explains why the internal salt concentration of fish are relatively high. This mineral concentration difference between the freshwater and the fish induce a constant osmosis force of the water trying to penetrate into the fish and the fish constantly need to compensate this force. Doing so, the fish is constantly consuming energy to compensate the osmosis. By adding a reasonable quantity of salt into the water, the mineral concentration delta between the fish and the water will decrease and therefore the osmosis stress will also decrease. There is a limit into the quantity of salt that we can add into our aquaponics setup. Indeed some plants such as the strawberries are very sensitive to salt and will be disturbed if the concentration goes over 5g/Litre. At Melbourne Aquaponics I use and recommend a concentration of 3g/Litre of water which means that if your aquaponics setup contains 1000Litres of water you can add 3kg of salt. This addition of salt will improve your fish comfort and will also reduce the fish fungus likelihoods. Fungus are a type of parasite that can develop on the surface of the fish. They generally grow on weak fish, they are contagious and are slowly eating the fish until it dies. You may wonder how to recognize the fish fungus but it is very specific. It forms a white coat on the skin of the fish. There are different species of fungus and they can be adapted to either freshwater or salt water. When a fungus develop on freshwater fish, a salt bath will generally help. This is the recommended disease treatment to be used in order save your fish from fungus attack. It’s an efficient home remedy.
As explained before we are limited into the concentration of salt we can add into our aquaponics system because of the plants. If your fish develop fungus you can simply fish and deep them into a specific bucket or tank that is not linked to your aquaponics system. Into this bucket you can increase the salt concentration up to 10g/Litre. Place an air stone into the bucket and you can then transfer your fish from the fish tank to the salt bath. Once your fish are swimming into the salt bath you must keep an eye on them as they will be submitted to a choc, you want to make sure they are still comfortable and survive. After 1 hour you can transfer your fish back into the fish tank.
The week following this operation you will have a close look at your fish to see if you can spot some remaining fungus and see the evolution.
If they are not going better you can renew the operation. Simply keep in mind that each time you renew this treatment, the fish are stressed and they consume energy so try to limit the number of treatments.
PS: While the fish are into the salt bath, the weaker fish highly affected by the fungus may start to feel unwell and turn their body on the side. You will need to fish them away and isolate them into a specific tank not connected to the rest of your aquaponics system where you will be able to take care of them and try to save them without contaminating the other fish.