Types of Fish Diseases
- Topical bacterial infections -These include fin rot, ulcers, pop eye and gill disease. They're easy to spot because they immediately cause damage to the outside of an infected fish's body, but they can progress fast and require prompt treatment with an antibiotic. They may leave survivors with lasting wounds. You should be aware that wounded fish may later be subject to bullying. Steroid-based treatments like Melafix can help some wounds to heal.
- Internal bacterial infections -These can be difficult to detect. Often the only noticeable change is in the fish's behaviour. You should consider them a possibility if your fish become listless or suddenly grow darker in colour, if their bodies swell, or if they die without any apparent symptoms. If this is the case, you should intervene immediately with a strong antibiotic.
- Fungal infections -These affect the skin and gills of fish, especially after injury, and they may occur as a secondary infection following another illness. Antibiotics can help fish to fight off fungus in some cases, but often the most effective treatment is methylene blue, which can be used either as a bath (for quick dips) or as a systemic water treatment.
- Parasites - Only very occasionally large enough to be seen directly, these are often detectable only through the affected fish's behaviour - flicking and rubbing to try and dislodge them. Some cause skin wounds or cysts, as in the well known 'white spot' disease. They can usually be treated with malachite green. However, in the case of parasites which form cysts, you'll need to dose this carefully to catch them during the free-swimming stage of their life cycle.