When diagnosing fish diseases it is important to consider the reasons which may have caused the fish to become ill. There are almost always pathogens (disease causing organisms) present in a pond, but a healthy fish that is well-cared for will normally be able to fight off most diseases.

The number one aim for any fish keeper should be to avoid causing stress to their fish. As a fish’s stress levels rise, its immune system begins to weaken and the fish will become prone to illness. It is estimated that up to 90% of diseases in pond fish are avoidable, and have arisen from poor husbandry.

Causes of stress in fish can be;

• Water parameters – sudden fluctuations in pH, or rises in ammonia or nitrite. This could be a result of over feeding or poor filter maintenance. Sudden temperature changes can also be a cause of stress in pond fish.

• Malnutrition – underfeeding, or feeding incorrect or cheap foods.

• Chemical pollution – can be caused by run-off from pesticides used in the garden, or chlorine from tap water.

• Predators– the presence of active predators, such as herons, will definitely cause the fish to become stressed, but even a pet dog or cat looking into the pond could be perceived by the pond fish as a predator (usually!).

• Mishandling – transporting can often result in the fish becoming stressed. Netting and bagging properly will keep this stress to a minimum, but fish should never be over handled.

It is important to eliminate the causes of stress before any resulting disease can be properly cured.The onset of stress may affect the fish’s colouration, feeding or usual behaviour. Many of these behavioural changes will only be recognised if the healthy fish are watched daily and you are familiar with their usual activities.Once the cause of stress has been determined and dealt with, any resulting illness can then be treated.