Why Koi Don't Grow

Posted on the NI web board, 6/20/2002, 10:08 pm

We are all pretty much interested in getting koi to the largest size possible for showing or just for the challenge and satisfaction of having a koi reach her full potential. The reasons a koi may not grow for you are due to water temperature, genetics, age, stress, oxygen levels, water quality, water parameters, feeding/diet and stocking levels.

Temperature? Easy. A warm summer of 74-80 degrees F. And cooler winter water temperature of 50- 60 degrees.

Genetics? Can't make a koi grow if it doesn't have the genetic program to be 70cm.

Age? Koi grow by the greatest percentage between birth and 4 years old. These are the years when very little can go wrong or you loose valuable "wonder bread" years. Koi can play catch- up in years one,two and three but slow, steady continuous growth is always best.

Sex also is important here, males simply not growing as large as females.

Stress? Causes large amounts of steroids to slow growth over time as only vital metabolic functions are maintained.

Oxygen? Needed for all major metabolic functions. Saturated oxygen levels for corresponding temperatures are key.

Diet? Depending on time of the year and water temperature, the diet will be the main component in growth. Protein levels are necessary to cause growth hormones to be generated and build cells.

Water quality? Like oxygen, water quality will assure normal metabolic function and keep stress from becoming an issue.

Water parameters? Ammonia,nitrite and nitrate will all effect growth. A lot has been said and written about sex hormones as the key to lack of growth in closed systems. This is partly true, but more influential is sexual maturity and its resulting effect on growth. The presence of sex hormones is an interference in the growth model and valuable time can be lost if females are diverting energy to egg production/breeding and egg absorption. A real case can be made for growth inhibiting hormones directly effecting population growth in a highly stocked pond. Water changes are the only way I know of diluting the hormonal signal within the water column. Diet( protein levels) will increase the production of both growth hormones and growth inhibiting hormones. And this feedback system is in competition with the sexual cycle and those hormones and steroids. This is why single sex ponds give the best results in terms of growth.

The last factor and perhaps the Biggest factor (in practical terms) in encouraging growth and general long term health, is in the area of an over-active biofilter. As you know, nitrification is an oxidation processes whereby two species (usually more in the real world) convert toxic ammonia to slightly less toxic nitrite and finally to least toxic nitrate. A very active filter will keep ammonia and nitrite to undetectable levels. But as "harmless" nitrate levels rise within the environment, some nitrate is found in the koi's intestines. The anaerobic bacteria, which is natural to the gut as part of the overall digestion process, denitrifies the nitrate to nitrite within the walls of the intestines. This has the effect of raising nitrite levels in the blood.,The effect of this chronic nitrite level affects the koi in several ways. Typically, you will notice buff-colored, drab skin. Over time you will notice poor growth rates.

Simple Remedy - Do frequent small water changes, use large amounts of aeration and towers for degassing, and flush the vortex daily during the warm growing season.

My humble two cents worth.

JR

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