Spawning - home bru

When in your last newsletter you remarked about countless eggs and the many thousands of babies forthcoming, I felt a surge of melancholy

because I knew that before long the tears of joy will be changed into tears of sadness as home breeders fiercely try to prevent the once healthy spawn from “dying before your eyes”.  A comment by someone receiving his latest newsletter from his local koi club. 

I want to share that feeling and elaborate.

The “you“ I am referring to is of cause the collective you engaging in happy spawning activity at home. Please do not take this personally, but I need to be quiet graphic in order to bring my point across.  Spawning at home is a most rewarding activity for a koi keeper. It is the time of the year he gets all excited about the prospect of many beautiful babies. Unfortunately it is also the time of disappointment to see hopes dashed.

If your fry are dying, there is clearly something wrong. In fact, if your fry are not dying but have not reached a good 30-50 mm by the age of 30-60 days, things are still wrong. But it can be remedied and you must be prepared to take the punch with it.

In June 1999, at the 18th Annual AKCA Seminar in Orange County, I tried to demonstrate mathematically, how the biomass increases in a spawning tank/dam over the first 30 days, and how the water quality deteriorates to the point of no return.   Obviously, my English was not good enough.

Fry can and should grow at 1-2 mm per day over the first 30 days. An average spawn from a 50-60 cm female is 400,000-500,000  eggs. You even venture to use two males to gain an 80%-plus fertilization rate. Now imagine you gain 300,000 fertilized eggs and let them hatch in a “generous” 3000 liter tank with air and no or limited filtration. Now, say it was possible and only 50% of the fry dies from malnutrition that leaves us with 150,000 fry. Say it was possible, that they reach 30mm by day 30, then they will weight only 0.5 gram each, but 150,000 fry at 0.5 gram is 75kg! I said “if it was possible” It cannot be, because by now we have TORTURED them to a slow death.

It cannot be because 75kg baby koi is equivalent to about 75 grown koi, 40-50 cm in length, swimming in your pond and being fed 3-4 kg per day of a rich 45-50% protein diet. Think of the 20-30kg bucket of waste produced, both solid and soluble (ammonia). Think of all the oxygen required (fish and pond). No. They will slow their growth, get sick from all the stress and malnutrition, and die off long before that can happen. You can try as you like to raise a full spawn in a small tank – you will only have a few survivors left, and only if you are lucky.

Friends, what you have to do is plan for the final outcome, not the beginning, but the end. You want to do your first culling in 30-50 days. How big should they be then? 30-100mm How much fish can I accommodate at that size at that time. Then limit the number of hatching eggs to that number. If it is 100, or 2000, or whatever, let it be and discard ALL the rest of the eggs. Hatch only that number and stick to your intention. Rather have 2000 healthy swimming fish at culling time than skimming of thousands of dead, belly-up fry that had a miserable life. I advise 100 eggs per 1000 liter, but feeding is a whole other matter and just as important. And of cause counting the eggs...

You will save yourself much on fruitless medication, and you will end up a much happier person.

Servaas de Kock
31/1/2013 updated 10/7/2017