How Big do Koi Grow? How Fast do Koi Grow?

Page Summary:  If you ever talk to anybody about fish be it fish keeping or fishing for fish the first question is always... How big was the fish or fishes? Koi, trout, roach, perch, sharks or whatever the species of fish hardly matters. It appears that like in so many other human endeavours size counts. This reminds me of my own fishing days long gone when asked by a curious passer by or enthralled onlooker ... Have you caught any? The answer was yes youre the third one today.

Koi are Coloured Carp.

Koi are Carp After All. Koi Grow Big and They Grow Fast Under the Right Pond Conditions and Feeding Regime

As much as Koi are capable of growing to significant size most koi will be confined to a maximum size constrained by their pond environment. Your pond of 5000 litres is not going to allow a koi to grow massively.

Extra large koi are called Jumbo Koi and frankly many are not just big fish but they are fat and disfigured fish.

For koi to grow large and remain fit and sleek requires a large pond, a top class feeding regime and filtration system and a mechanism for the koi to exercise themselves. In this regard top koi keepers induce currents in their pond so that their koi can exercise swimming against the current!

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Spawning Brush

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How Fast do Koi Grow? Improving Growth of Your Koi

No two koi behave the same in identical living conditions since there is a critically important genetic component to the final mass and rate of growth of the koi fish to achieve that optimum mass.

Its important to optimise the living conditions and environment and to provide the correct feeding regime. A well designed "proper" koi pond with first class biofiltration systems principally based on the traditional Vortex settling chamber and vortex biofilter units are ideally suited for conditions in which high growth rates can be obtained. These mechanical and bio filtration "plants", for thats what a well designed koi pond vortex filter system really is, have to be well maintained to allow optimum water quality conditions for the koi fish daily living.

Meticulous draining of bio filter systems on a daily basis (maybe more) is required to provide perfect water quality and ideal growth systems.

Even the most perfectly designed koi pond and koi pond equipment will not allow for any koi to grow to its optimum size becasue there are many other factors at play in determining how big and how fast a koi will grow.

In this respect genetics plays a vitally important role and the real world class jumbo koi start life as hand picked fry.

By the way its impossible to look at a small koi with amazing and magnificent colours and forecast that the same colours and patterns will apply as the fish grows. In fact this is rarely the case which means agonising over the selection of those beautifully marked 4 inch long koi at the dealers can be a complete an d utter waste of time and money.

Koi dealers sell koi fish to the unsophisticated koi buyer by portraying colour and colour distribution along with koi length or mass as major price determining points. The fact is the present (colour and design) is no indication of the future (colour markings and design).

Anyway back to growing koi for the average koi pond keeper and not the koi krazy keepers which is how the koi fraternity do like to see themselves.

a. Genetic make up b. Environment (stocking density, temperature, water quality etc) c. Diet

We cannot influence the genetic make up of the koi in our collection as this is already fixed and determined, so we can only enhance growth by managing either their environment or their diet.

How Fast Do Koi Grow? Keep a Low Stocking Density

  • Its simple.. the larger the ratio of pond water mass to koi mass the better will be the conditions for growth. This is described a maintaining a low stocking density. If you think you have too many fish in the pond then you probably have.
  • Maintenance of the correct and optimum temperatures year round will significantly improve chances of growing large koi.
  • High quality high protein fish foods of 35%+ fed in correct quantities regularly rather than in big single servings will optimise the feeding regime to optimise growth of the koi. This will reduce ammonia "spikes" as they are referred to ... ie an initial and rapid increase in ammonia concentration in the pond water shortly after feeding. So little and often is the rule for correct feeding of koi
  • Biofiltration performance must be excellent 24/7 to ensure no knock-backs due to ammonia or nitrite levels being present on an ongoing basis.
  • Maintaining an optimum water temperature year round since this determines appetite of fish and ability to metabolise. Temperatures in summer months can be as high as between 25 and 27 degrees C whilst temperatures in winter should be controlled at around a temperature of about 15 to 17. Rapid and sharp swings in temperatures should always be avoided. Like most things in life a degree of stability is important.
  • The need for an ultra efficient high capacity koi biofilter is critical. The performance of a biofilter can be dramatically improved by injecting air into the biofilter itself or in the water stream entering the biofilter system. This is one reason why a well designed Vortex filtration system works so well. Air stones are suspended into the upper layers of the vortex unit close to the Japanese matting matrix generally used in these high efficiency well proven koi filter systems. THis intimate mixing of air and water provides ideal conditions for mass transfer to take place and this is the process that drives conversion of ammonia to nitrates.
  • Healthy, stress-free fish are fast growing fish. Adequate solids removal and biofiltration are essential to maintain good water chemistry. One significant factor that has been shown to improve growth (as well as biofiltration) is vigorous aeration. Tests have shown that fish convert their diet into fish tissue far more efficiently when dissolved oxygen in the pond is highest.
  • There is an optimum rate of feeding fish food but once again the number presented always depend on this that or the other so take them with a pinch of salt. For this reason I have not stipulated any numbers. As an aside these numbers are expressed as a % of body mass of the fish... but how do you know the mass of fish in a pond containing a variety of sizes and shapes?

For me theres a golden rule in koi keeping and its a rule that applies generally... whenever youre told something which sounds like its straight from the koi gospel ask why and then test the reply by using a chunk of common sense. My favourite bit of koi bunkum is that a bio filter must be 1/3rd the pond volume.

You know whats important for readers of my articles... its not the size of the koi or how big the koi will grow. Its much simpler. Are you enjoying your fish and are you learning about ponds and pond keeping for the pure pleasure of it? Lets face it were not going to set any world records for the biggest koi and who wants to anyway?

Other articles about koi and fish pond care in winter

Pond Heaters. Heating koi ponds winter growth feeding benefits

Koi pond heating using gas electric in UK temperature control

Bringing fish and pond and water out of winter into spring

Koi goldfish pond covers over winter. How to look after pondfish

Over-wintering koi goldfish hibernation cold freezing water ice

Koi pond heating using gas electric in UK temperature control

Should I heat my new koi pond this winter. What temperature?

Temperature swings. Koi Goldfish Feeding & water temperature

To Feed or not to feed your pond fish or koi or goldfish

How Do I care For My Garden Fish Pond In Cold Winter

Frozen Koi Ponds & Fish Ponds. Ponds Freeze in Winter. Pond Care in Freezing Winter Weather

Interpet Koi Pond Test KitWhat the Does pH of Koi Pond Water Mean? Should I measure Pond pH