Fish are often victims of parasitic attack when they are either under stress, wounded or are living in crowded conditions. Aquarium fish can be susceptible to parasites for a variety of reasons, including poor water quality, over-crowding and injury.

Many parasitic problems in fish tanks are due to an increased number of protozoas in the water. Protozoas are single cells organisms which feed off dead skin cells on the fish’s body. They can also be ingested and feed off bacteria in the fish’s gut and the mucus on the gills and skin. Some species can puncture the fish’s skin and feed off the body fluids. Protozoas can create significant problems in their own right, they can also be the precursor to other diseases by the transfer of pathogens from their own bodies and through infection from the puncture wounds they inflict.

Protozoas are naturally occurring and they usually don’t bother fish unless their numbers increase. In most cases this will be due to a build up of organic matter in the tank due to over-crowding or over-feeding. They are also easily transferred from one to tank to another by the use of nets and tubes.

A fish which is suffering from a protozoan infection will usually have skin and gill problems and this can be identified by the rapid breathing and the rubbing of its body against rocks and plants.

Bacterial diseases are extremely common in aquarium fish and can be difficult to diagnose without the aid of a veterinarian. Bacterial infections tend to cause a range of different symptoms making the specific identification difficult, however if you catch the infection early, anti-bacterial formulas from aquarium shops can assist in the fish’s recovery. With bacterial infections there are a few key symptoms to check. A pot-belly is the swelling of the fish’s abdomen and is indicative of a systemic infection which has resulted in the swelling of internal organs. This may also cause the fish to have problems swimming. Uneven scales can be an indication that a bacterial infection is present with raised or missing scales a key indicator. These vulnerable areas on the fish’s body can also leave it susceptible to other infections.