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8 ways to kill your koi

Koi keeping is an increasingly popular hobby. The fish are fascinating and provide a colourful addition to any garden. But while koi are hardy fish which are well-adapted to living in a variety of climates, they do have specific needs. If you are new to keeping koi, it is easy to make mistakes and to fall short of meeting the basic needs of the fish. Here’s eight ways that you could kill your koi.

  1. Pesticides
    We know that you wouldn’t deliberately pollute your pond with pesticides. However, in heavy rain, runoff can find its way into your pond water and bring pesticides from the environment with it. It is important to allow for this fact when planning the construction of your pond and you may need to create a means of diverting runoff away from it.
  1. Infections
    Koi can fall prey to viral or bacterial infections. They can generally fight these off but it is important to maintain good water quality and to provide your fish with the correct diet. Keep an eye out for signs that your fish are unwell and act quickly if you have concerns.
  1. Jumping
    Koi are natural athletes and may even appear to be suicidal at times! They can and do jump and if they miss the water on the way down, they could perish before you discover that there is a problem. If one of your fish is a persistent jumper, installing a bird net might be a good idea.
  1. Lack of oxygen
    Keep an eye on the growth of your fish because competition for supplies is the most common reason for oxygen deprivation. You should stock your pond with the correct number of fish for its size and consider featuring plants to boost oxygen levels. As the fish grow, their oxygen consumption increases. A nicely balanced pond environment can soon become a dangerous one for your stock.
  1. Predators
    Your fish represent an inviting meal for predators and they will be persistent in their attempts to get it. You will probably need a bird net and fencing around the pond. If you don’t protect your fish you will soon find them disappearing. Once a predator has found out how to access your pond they will keep coming back.
  1. Ulcers
    Koi rest on the bottom of the pond in winter and so their undersides are in contact with any substrate. Their bodies could become ulcerated as a result and so it is best if the bottom of the pond is smooth.
  1. Parasites
    Koi can be afflicted by parasitic infections. Unfortunately, by the time the koi exhibit visible symptoms, an infection may already be severe. Most infections are easily treatable so the key to success is to carefully monitor the fish for signs that they are failing to thrive. Look out for listless fish, koi which have lost their vibrancy and individuals which will not eat.
  1. Poor Water Quality
    The number one cause of koi death in ponds is poor water quality. Always ensure that your filtration system is working well, regularly test your water and don’t overstock the pond.


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