Rookie Mistake & Fry Cold Tolerance

[Coldspringsfarm]

So I was gearing up for a spawning attempt with a pair of Shusui this season. Last year they didn't attempt spawn until the first week of May so I thought I had time. I was wrong. Went out late morning several days ago and immediately smelled spawn and saw foam on the surface of the tank. I was so disgusted with myself for not separating the female. One of the males was huge and obviously has gorged himself on eggs. I could see some eggs above water surface and sporadically stuck to walls, so I moved the fish out in hopes of saving what I could. Fast forward to today(day 3) and I appear to have hundreds of hatched fry!

My main question right now is this: What is the cold tolerance of koi fry? They are in a 250 gal tank with current water temp around 65-68 degrees, but a cold front comes through tonight with lows in the mid 40's overnight. Mid 60's forecasted as daytime highs. I think I have 2 nights of this before temps recover. I already added an under powered tank heater(300 watt I think), but should I try to further insulate?
Pic of a few fry under microscope.

[Coldspringsfarm]

Quick update. I did a halfway insulation job last lastnight with some scrap foam board I had. I also threw some bubble wrap on the water surface to offer a bit more insulation. The low air temp got to 48 lastnight and the water was around 64. One more night of cool air tonight and I may be out of the "woods".

[Matt24]

I've had fry make it through water temps in the low 60's F and upper 50's F a few times and have never lost a batch of fry to cold. One group of fry even made it through 55 F water when they were 4 days after hatching. [I did get an unusually high number of deformities in that spawn, though I doubt the cold was related.] I suspect these will not be harmed by the temps.

But what you are doing to insulate to slow the drop of water temp sounds like a reasonable precaution. I was about to suggest covering with plastic sheeting while air temps were dropping into the 40s.

[Coldspringsfarm]

Thanks for the reassurance! Tonight will be colder with a predicted low of around 42. I wrapped the entire tank in moving blankets. They should be snug as a bug!��. The water held steady around 64 all day today.

[Matt24]

Hope you’ll get some good results from this spawning and will update us on their progress in the Amateur Breeders Forum.

[spkennyva]

You don't mention the filtration you're using. A 250 gallon tank without a good bio filter can go toxic pretty quickly. Careful monitoring of water parameters is super important. As Matt mentioned, start a thread on the Amateur Breeders Forum.

Best of luck!

[Coldspringsfarm]

Hope you’ll get some good results from this spawning and will update us on their progress in the Amateur Breeders Forum.

I actually started the thread in that forum and the admin moved it to main thread for visibility. I will probably keep updating this thread, but if someone wants to move it back I am fine with that. Not sure I can do it myself.

[Coldspringsfarm]

You don't mention the filtration you're using. A 250 gallon tank without a good bio filter can go toxic pretty quickly. Careful monitoring of water parameters is super important. As Matt mentioned, start a thread on the Amateur Breeders Forum.

Best of luck!

The system is a total of about 750 gallons. It's a series of 3 ibc totes connected 60 gallons of K1 media barrels. 30 gallons is static media and the other 30 is MBBR. There is some additional fish load with the parent koi in one of the other IBC totes but they are getting moved to my newly built koi pond this weekend. The accidental spawn sorta tied my hands at
the moment, but I have options when the time is right to move them. Set up a 1500 gallon kiddie pool a few days ago. I have a 10x30 mud pond I dug last year for just this occasion. I also have a 3/4 acre pond that I am considering doing some cage culture. This is all complicated by the fact that 2 Kohaku breeders should be delivered next week and I fully intend to let them spawn. I bought them when I thought my Shusui spawn failed.😂. Glutton for punishment!

[Coldspringsfarm]

Quick overall update. The Shusui fry seem to be doing well. The water temp got down to about 58 night before last and has recovered to around 62 since then. The swim up started about 48 hours ago and today I would estimate about 75% are free swimming. I started spoon feeding a mix of chicken egg yolk and aquamax fry powder in liquid suspension. I had pre-sifted the fry powder with an 80 mesh screen so the largest particle size should be about 180 microns. I have been able to visibly witness the fry eating particles today, and by midday I could see full bellies on some of them. Of course, I had to throw one under a microscope to get a better look. Pics attached. The free swimming really makes it look like a lot more fish. I am still estimating around 1000 fry but that is a very rough estimate.



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