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8 Ways to Kill Your Koi (And How to Avoid Them!)

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Koi are a beautiful addition to any water garden:


Koi keeping has become an extremely popular hobby among water garden enthusiasts.  They are a colorful addition to any outdoor space and can quickly become a conversational piece due to their quirky and often comedic personalities.  Koi are an especially hardy breed of fish, making them well suited to living in just about any climatic condition as long as proper care is taken to meet their most basic needs.  However, there are some sure fire ways to kill your koi.  Knowing what these are and how to avoid them will ensure that you have a long and harmonious relationship with your fish.  Let’s take a look at them from the least deadly to the most lethal.

8).Pesticides– Conscientious pond keepers like yourself will refrain from purposely introducing toxic substances into your water garden environment.  But, heavy rains cause runoff which can find its way into your pond, killing your fish.  Proper planning during the pond construction phase will reduce the amount of runoff your pond will be subjected to and decrease the amount of money you will spend restocking your pond every few months.  However, if you find that your pond does experience the effects of runoff after a good rain, it would be a good idea to design a drainage system that will divert the water in another direction, away from your pond.

7). Viral/Bacterial Infections– Koi are not immune from viral or bacterial infections, though most can fight them off fairly well as long as they are in good health.  Maintaining optimum water quality, preventing injury by removing sharp edged rocks, and providing a well balanced diet will go a long way to ensuring that your koi stay infection-free.

6). Jumping Out– This is a situation that generally affects novice koi keepers as more experienced keepers have usually experienced their fair share of suicidal fish.  Whether they are chasing each other, chasing a meal, or are simply not happy with their current environment, koi are notorious jumpers.  Ask anyone who has ever tried to keep a koi in an aquarium without a lid.  Most often, the fish will jump and land safely back into the water, but some are not so lucky.  Unless you have someone standing watch at all times, it’s almost impossible to prevent every death due to an overzealous acrobat in your pond.  If you do find yourself with a jumper, you might think about installing a bird net.

5). Lack of Oxygen– This is also a common novice mistake, but can strike even the most experienced koi keepers who might not be keeping tabs on the growth of their fish closely enough.  The most common reason for lack of oxygen in pond water is competition for resources.  Balancing your pond with the right number of fish, the right number of plants, and artificial oxygen sources is tough.  What’s even worse is that this is also an ever changing situation.  Why?  Because as koi grow, their demand for oxygen increases as well.  For example, a pond can be balanced in the spring with 6- 3” fish.  As the season progresses, these fish can double in size, placing a strain on the existing resources.  If additional oxygen isn’t added or some of the fish removed, you risk losing the whole lot due to oxygen deprivation.  The best way to keep this situation in check is to plan ahead and anticipate your pond’s ability to support much larger fish and stock accordingly.

4). Predators– Koi, just like most other fish, are on the menu for a whole host of local wildlife, from your neighbor’s curious feline to that really strange looking bird you’ve seen standing in your pond to that harmless looking frog peering out from under the water.  These guys aren’t here to enjoy the beauty of your water garden.  They are here because your pond has created an easy meal.  Keeping your fish safe from predation can be a full time job, but is well worth the effort.  In many cases, a bird net and a decorative fence will keep most hungry animals at bay.

3). Ulcers– Koi tend to rest on the bottom of the pond during colder seasons which will allow their soft bellies to have prolonged contact with the substrate you have at the bottom of the pond.  If you happen to have gravel or rocks lining your pond, this can cause injury, which can ulcerate and become infected, ultimately killing your koi.  Smooth bottom ponds are preferred by many koi keepers for this reason alone. The easiest solution for avoiding this situation is to not use gravel or rocks as a pond liner.

2). Parasites.  All living organisms are prone to developing a parasitic infection and koi are no exception.  The bad news about parasites is that you will rarely know there is a problem until your fish begin exhibiting symptoms, which usually indicates that there is a somewhat severe infection.  The good news is that most parasitic infections are easily treated with a carefully controlled regimen of anti-parasitic medication introduced into the water.  The key to avoiding koi death due to parasites is to recognize a fish that is not thriving.  Koi that do not eat, that are listless or that have lost color vibrancy should be checked for parasites.

1). Poor Water Quality– The number one cause of koi death is poor water quality.  The quality of the water your fish live in will ultimately determine how long the fish will live.  Proper filtration, regular testing and maintaining proper numbers of fish in the pond all figure into the equation.

So, there you have it.  By keeping these things in mind while caring for your koi, you will be well ahead of the curve when it comes to keeping them healthy, happy and alive.  Water quality is the most important aspect of caring for koi, so make sure you don’t overstock your pond, have plenty of oxygenating plants that will add valuable oxygen as well as break down fish waste, and filter, filter, filter.  Good luck and happy koi keeping!

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