Treating fish diseases before they arise


About 90 % of all fish diseases are the result of a weakening of the immune system. This may be caused by:


The first priority is to check that the food meets the nutritional requirements of the fish and that it has been adapted to them. You can find a summary of who eats what under Het juiste voer voor uw vissen . Additional variety with natural food, such as PlanktonPur can increase the well-being of the fish considerably. Each food needs to be used up within 3 months after opening. After this the vitamin content is too low and the body can’t build up any defences anymore. But incorrect storage (humid, warm or in sunlight) can also reduce the quality of the food. We therefore recommend you only buy the amount of food you are able to feed within 3 months. You can additionally enrich the food with vitamins ( JBL Atvitol ) Even then the food needs to be used up in the time period mentioned. Imagine it is a tin of biscuits lying around “open” for 3 months.

Water values

Each fish has its demands on the water parameters. We are looking at the general hardness and the pH value here. Anyone who gets deeper into the subject will also develop a greater awareness of conductance, flow conditions, lighting factors and lighting periods. If these factors are unsuitable for fish, they will be constantly under stress. This will lead to a weakening of the immune system and the fish falling ill. Fish well-being can also be influenced by such issues as the mineral balance (KH and GH) of the water. An imbalance (with low values) can lead to deficiency symptoms and diseases, such as the hole-in-the-head disease. The most common cause of illness in fish is the presence of small amounts of toxic substances in the water which is not enough to kill the fish, but enough to cause them stress. These substances include nitrite, ammonia, and also copper, chlorine and heavy metals. We always recommend you use a water conditioner ( JBL Biotopol ) when changing the water and when checking the most important parameters ( JBL ProScan ). Nitrite is a frequent problem, especially after rigorous cleaning. To prevent an imbalance of nutrients, such as nitrate and phosphate, you need to change 30% of the water every 7-10 days.

Fish stock and equipment

Harmonious stocking ensures the well-being of the fish. Under frequent territorial conflicts or physical attacks the animals not only become stressed but also often suffer serious injuries. These wounds often can’t heal properly because the additional stress has weakened the fishes’ immune system. Therefore please ensure that the fish are always in a large enough aquarium and that the species harmonise. The equipment and the design can also make a huge difference. If a species establishes a territory or prefers caves these need to be provided in adequate numbers. Creating stone constructions or providing dense planting for the fish to retreat in can also help to support the interaction of the fish.

New fish

Adding new fish into an existing aquarium rarely causes problems. Taking the precautionary measure of quarantine beforehand has proven to be beneficial. Unfortunately problems do sometimes occur, even though the fish were healthy at the pet shop. Illness can arise at any time in the newly added fish after the stress of transport. Sometimes it is even the other way round and it’s not the new animals who fall ill but the previous fish stock. This is due to the fact that the new fish bring along unknown parasites or pathogen bacteria, which are unknown to the immune system of the established fish. Even though they are still healthy the established fish have to develop a new “defence technique” against these unknown threats very quickly. If, because of one of the factors mentioned above, they don’t manage in time, their defence is weak and they fall ill. A healthy fish is able to cope quickly with the newcomer.

If your fish fall ill despite all the precautionary measures, it is first important to determine the symptoms of the disease. Knowing them enables you to carry out a first diagnosis. For this purpose we have provided you with the Online Hospital with over 500 pictures and a guide. This will give you important information about the disease and possible solutions. If the diagnosis is then still unclear, consult a vet or let another fish expert examine the smears under the microscope. This is the only way to get a reliable diagnosis and as a result to combat the disease successfully.

But remember: immediate action is required at the first signs of a disease. Waiting too long can result in one single “dot” reproducing massively and infecting all the fish. The risk of infection increases within a short time. Even if you have read otherwise, the prophylactic use of remedies should strictly be avoided. This creates resistance and the fish are permanently exposed to the active substances.

Please be aware that although the use of remedies combats pathogens it only rarely eliminates the cause, as explained above. It is therefore always important to find the cause to avoid a relapse. After all, we are talking about the welfare of your fish.

© 21.09.2015
Matthias Wiesensee
Matthias Wiesensee
M.Sc. Wirtschaftsinformatik
JBL GmbH & Co. KG
