[Fishbreeder]

My oldest koi is a doitsu sanke, 38 years old and going strong. Actually Methusela for a koi, mostly my breeding koi have an average life span of from 7 to 10 years. Generally speaking, breeding koi are depreciated and replaced on a five year program (in Japan too).

You can get an idea of age by reading scales. But....it is a technique poorly understood and primarily used in the context of aging a cohort (group of fish the same age) and not individuals. Scale rings grow faster or slower depending on many things, food climate, etc. Within the rings there are circuli-the many rings deposited during growth and annuli-rings that are only deposited as growth rapidly slows with the onset of winter. If you take several scales from several fish of similar size from a large group, you can indeed gain inference as to the age in years of the group of fish. Not so easy to determine the age in years of each fish.

Now, some fish have an otolith (ear stone) which can be cut and rings counted to get a better idea of the individual fish' age. Study of bones in the spine and other clues as to age can also be considered.

I know of no koi being documented to live over 100 years. I know of one common carp at a fishing camp in the UK that was well documented to have lived 99 years.

Not koi, but antoher species, largemouth bass (Micropterus salmoides) has been studied extensively as to growht in different situations. It is well documented that bass living in a powerplant cooling reservoir (stays warm all year long) grow much faster than those in adjacent, but unheated reservoirs. However, they tend to live shorter lives and never reach as large an overall size as those undergoing a "four seasons" lifestyle.

My guess is that koi would tend to be similar to the bass. If heated constantly and pushed hard with feed for maximum growth, they will grow faster, but live longer and get to a larger ultimate size, I doubt it.

Brett