What Is Going On In Your Fish Pond
We watch our fish swimming around the pond all day. From year to year they get a bit bigger, plumper and more friendly. All day long they breathe and have to digest food to get bigger. Here’s a bit more of an insight of what’s happening in that watery environment each and every day.
Fish breathe in through the mouth and out through the gills …… In this way oxygen enriched water is passed across complex structures and cavities containing myriads of blood vessels. As the water crosses these blood containing structures the oxygen is removed from the water.
A bit of classical chemical engineering takes place here. Blood circulating through the gill system tends to pass in what is called counter-current direction to the oxygen enriched water. Some of you may recall my cup of coffee article explaining bio-filtration principles and something similar is happening here. In simple terms the oxygen concentration in the water must exceed that in the bloodstream for oxygen to leave the water and pass through the gills into the fish’s circulating system.
This is why oxygen depleted blood is the first to come into contact with oxygen enriched water (at the gills). The fish actually takes in water simultaneously which it later excretes through the kidneys.
As this counter current process is taking place nitrogen containing chemicals pass from the blood stream out into the the circulating water via the gills. These chemicals show up as ammonia which is removed by bio-filtration and is the primary reason for needing a bio-filter if you keep fish since even small concentrations of ammonia are poisonous.
Koi Digestion and Growth
Koi have teeth, yes.
The food they take in is “ground up” to some extent. They are also able to remove planktonic or tiny food particles by filtration. Food passes into what is essentially a tube with waste products coming out of the back end after nutrient extraction using the so called stomach and relevant organs.
The ability to digest food is very poor and reduces significantly as temperature drops. This is reason retailers sell wheatgerm for winter feeding since it is supposed to be more digestible at the lower temperatures … I wonder??????
Koi in average situations will grow quite quickly until they reach an equilibrium state which to a large extent is determined not just by the amount of food ingested but also by the size, shape, depth and water movement within a pond environment. Nigel Caddock did some work on making koi swim against currents induced into a pond by jets of water to determine effects on growth, shape and body mass.
Small Ponds Cannot Produce Large Koi.
Under good pond circumstances it appears that a 1 year old koi could be about 12 cm (5 inches) or so and by the age of 10 could be as big as 70 cm ( 30 inches) depending upon its living environment over that period of time.
I’m not sure if this milestone has been reached yet but at one stage a massive prize was offered to the first koi keeper who could raise a kohaku (red and white only) koi to 1 metre length ( 39 inches). I do know this limit was approached on a few occasions.
The typical weight of a 70 cm koi would be around 5 kg in excellent condition ( 11 pounds). To buy a mainstream koi of 70cm length would cost a lot of money in any country. On the other hand most are not worth very much money unless bought from a well known dealer.
Koi can live very long lives … and in Japan some have lived close to 100 years.
Finally in this very basic introduction to koi let me suggest to you that nobody has any idea what a koi of say 1 year old will look like at 5 years of age even though some highly experienced breeders may be able to get close.
Consider this when someone tells you differently and also don’t fuss too much about selecting the 10 best from that tank of 400 small 2 inches long koi next time you take a visit to your dealer. And certainly do not pay more based upon a dealer’s belief that the fish will DEFINITELY be a winner.
On an aside the top Japanese breeders cull about 99% of all koi bred …. they do a basic inspection at lightning speed in an attempt to sieve out the best potential …. somehow.
