Types of Disease
Bacterial diseasesBacteria are present just about everywhere and can be useful, such as those which aid filtration, or harmful as in the case of bacterial diseases. Disease causing bacteria are always present in the aquarium and under normal conditions a fishes immune system will prevent any serious outbreaks. Common causes of bacterial disease are stress, bad water quality, entry through wounds, or introduction of already infected fish.
A bacterial infection can often be seen as a wasting or erosion of part of the body, or as ulcerations. In cases where the affected area is not visible the fish may show signs of distress such as not swimming with other fish, hiding away, becoming lethargic, loss of colour and unwillingness to feed.
Finding out which specific bacteria is causing problems in order to identify the best treatment is difficult, and may require a laboratory culture to be grown, which is beyond the realms of most fish keepers. Whilst there are a number of proprietary anti-bacterial treatments available in shops, they usually have a limited effect and should be regarded as an aid to the fishes own immune response. Because of this it is very important that fishes affected by bacterial problems are given the best possible environment to aid recovery.
Fungal diseasesThere are tens of thousands of species of fungus and vary in size from microscopic single celled organisms to large organisms like mushrooms and toadstools. Most funguses present in aquariums are normal, and are vital in the proper breakdown of waste material. Most funguses found on fish are also perfectly natural and feed of dead cells without harming the fish. Problems with fungal infections usually occur as a secondary infection when exposed or damaged tissue provides an area for fungal spores to take hold and infect living tissue. Some bacterial diseases such as mouth rot, fin rot or mouth fungus are mistakenly thought to be caused by a fungal infection.
Viral diseasesDiseases caused by viruses are a tricky problem for fish keepers since in most cases they cannot be directly treated, and if there is a treatment it is usually an expensive option only available from a vet or expert consultant. Viruses are tiny organisms, even smaller than bacteria, and live inside the hosts cells. Because of this, any chemical treatments that kill the virus must also kill the host cell, causing damage to the host. Some viruses can be treated with vaccinations but in most cases, like with the common cold (also a virus), the best that can be done is to treat the symptoms and allow the fishes own immune system to mount a defence.
Environmental diseasesThe term is sometimes used in different ways but here we can regard environmental diseases as symptoms caused as a direct result of an incorrect environment, rather than a disease causing agent such as a bacteria, fungus, or virus. Whilst an incorrect environment will create conditions that allow disease-causing agents to take hold, when we talk about environmental diseases, we are simply looking at the direct effects of environmental factors. Environmental diseases can be a result of bad water conditions such as an incorrect pH, hardness, or temperature or high levels of ammonia, nitrites, or nitrates. Other toxins such as heavy metals or chemicals can cause poisoning, either quickly or over a longer period. Stress can also be an environmental disease, and there may be multiple causes of stress in a typical aquarium.