Harmful Bacteria in a Fish Tank

Fish tanks contain not only good bacteria that break down ammonia into nitrates, but sometimes harmful bacteria as well. Harmful bacteria often cause diseases in fish that can lead to death if left untreated. Thoroughly cleaning your fish tank and equipment every week and putting new fish in a quarantine tank before introducing them to your fish tank should prevent these bacteria from infecting your tank and fish.

  1. Chondrococcus Columnaris

    • Chondrococcus columnaris enter fish tanks through infected water from other fish tanks or infected equipment like aquarium nets. This bacteria causes diseases such as fungus, mouth fungus and columnaris. All of these diseases cause white cotton-like substances to grow on the fish's mouth, body or fins. Fish with severe cases of mouth fungus sometimes cannot close their mouths and suffer from respiratory problems. Eliminating this bacteria in a fish tank typically involves treating the water with copper sulfate.

    Mycobacterium

    • Mycobacterium also enter fish tanks through contaminated water. This slow-growing bacteria causes diseases like tuberculosis in fish which leads to discoloration, skin lesions, bulging eyes, disfiguration, swelling and eventually death. All fish are susceptible to mycobacterium infections but malnourished fish seem to be more at risk of infection, according to the book ̶0;Fish Diseases and Disorders.̶1; The bacteria can also affect humans and typically causes sores or ulcers on the skin. Mycobacterium is usually treated by removing and treating the affected fish with medication and cleaning the fish tank and equipment with a bleach solution.

    Psuedoomonas

    • Like most harmful bacteria, Psuedoomonas usually enter fish tanks through infected water from other fish tanks or infected equipment like aquarium nets. This bacteria causes diseases like fin rot, mouth rot, rot and tail rot. These diseases eat away at the flesh on the tail, fin, mouth or body of the fish and cause it to decay. Rot diseases are more common in brightly-colored fish or fish with long tails, according to the book ̶0;Small Animal Care.̶1; Eliminating Psuedoomonas in the water typically involves adding copper sulfate to the water.

    Aeromonas

    • Aeromonas not only enter fish tanks through infected water from other aquariums but also by introducing infected fish into the tank. The bacteria spreads from one fish to another through direct contact. This bacteria typically only affects fish already weakened by other diseases or old age. It can cause diseases like Furnculosis which produce open sores on the fish. Aeromonas also cause Hemorrhagic Septicemia which produces red streaks on the fish's fins. Other diseases and illnesses caused by this bacteria include rot, mouth rot, fin rot and tail rot as well as skin lesions, ulcers and swollen bellies. Eliminating Aeromonas in the water also typically involves adding copper sulfate to the water.