Every year on the farm spawning time is an enjoyable yet stressful time of year because of the potential complications that can come with artificially spawning fish.
First of all the broodstock pond is netted and the best looking fattest females are picked and to every female you spawn 3 males are stripped to make sure the milt quality is good . Once the fish are picked they are taken to the hatchery separated and warmed up to between 18c-22c depending on species, once they have been warmed up over a 12 hour period they are injected with a synthetic hormone which induces the fishes brain to produce a spawning hormone from the pituitary gland…
Over a 16-30 hour period the females soften up and the males rough up and start to produce lots more milt, from 16 hours after the injection the females are checked to see if the eggs are running freely, as soon as they are the female is put into a tub with Koi calm and water in which sends the fish to sleep so it can be handled easily, once the fish is under the anaesthetic it is placed on a mat and put in a towel so it is completely dry to stop moisture from getting onto the eggs or milt, water is the trigger for eggs to start to swell and for milt to become motile without water fertilisation can’t take place. That’s why you strip the eggs from the female into a dry bowel and then you strip the male into the eggs and stir it together with a feather only at this point do you add a fertilisation solution which is urea and salt mixed in water. The eggs have a tiny hole in them called a micropile and that’s where the sperm enters the eggs, after 30 seconds off water being on the eggs the micropile closes and the egg starts to swell with water. If the sperm hasn’t entered the eggs within this 30 second period then the egg will not be fertilised and will fungus up and die.
You then stir the eggs with a feather gradually adding fertilisation solution for 1 hour until the eggs are fully swollen, the eggs then go through a de sticking process using a tanic acid solution which takes the sticky membrane away from the outside of the egg bit still keeps the egg intact. At this point the eggs are placed into the zugar jar and start slowly rotating in the flow of water.
The eggs will take 3-5 days to hatch off depending on species, over these days they are treated every 4-5 hours with an antifungal solution that is injected into the pipe that goes into the bottom of the zugar jar, this is because the dead eggs that weren’t fertilised have started to fungus up and then can spread fungus to the live eggs if you don’t take these precautions.
Once the eggs hatch off they sit on the side of the jar or tank and use their yolk sack for 2-5 days depending on species, once they have used up the yolk sack they have to swim up and fill their swim bladder so it’s important the fry can figure out which way is up and which way is down otherwise they can fail to inflate their swim bladder and die because they cannot control where they are in the water column this why the lights are left on. At this point they are actively looking for food and we feed them 4 times a day on Brine shrimp for 2-4 days and then they go into the farm ponds that have been fertilised 15-20 days prior so the fry have lots of natural food to eat for 2-4 weeks and then they are big enough to go onto a high protein pellet diet to optimise growth.
And so it begins life on the farm.