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Genetics question( guppies)


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I guess it depends on how far they’ve been line-bred already.

I think you can go 6-7 generations inbreeding livebearers without absolutely crippling the stock.

But most breeders would probably like to see additional genetics wound in by 4x generations.

It can be frustrating, because desirable traits become more pronounced as you selectively breed. By a 4th generation, you may be seeing peak traits in your line(s). Adding a fish from outside can “muddy the water.”

Remember that gravid female guppies hold milt from any male they’ve been with for a long, long time. If you go to a store and buy females, house them alone together awhile, they’ll likely box up and drop fry within a month or two. It may take time for females to prioritize the milt of a new male. So fry born should be separated from your colony until you are assured of strong genetics.

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On 7/9/2022 at 9:49 AM, Fishkeeper84 said:

Okay! Thank you for the advice. Greatly appreciated! 

I'm going to add to Fish Folk:

When I introduce new females, I keep them separated and then *separate their fry* because they will have fry. It will be the female fry of the newly bought females that I will introduce to a specific male, to test what the offspring look like, before adding to colony breeding.

Also, for line breeding:

You can take 6 brothers (this is a hypothetical breeding situation)

Put one brother each in his own tank (6 tanks)

Add the new female fry, 2 or 3 females, to 2 of the brothers.

Add established females to the other 4 brothers.

Every 3 months, evaluate your fry.

1. Are they healthy?

2. Are they true to your selected phenotype?

3. Have you been culling any who don't meet expectations?

4. Separate the fry into a female tank, a male tank, a yet to be determined tank, and get rid of your culls.

In a perfect world, you will be able to have a daughter tank and a son tank for each of your original 6 brothers (this is where huge breeding fish rooms come into play). If you can't, then put the sons from the 4 tanks that have established phenotype in a tank together/daughters from established phenotype together, and have a separate daughter/son set up for the two brothers who have "new blood" so you can evaluate how they grow, develop, and if they breed true.

Next, you can "retire" a set of established breeders, and put a "new blood male" in with 2 to 3 established phenotype females. This is how you get to test how solidly your livebearers are breeding true.

A solid line is when greater than 8 out of 10 replicate their parent's phenotype.

Alternatively, You can keep males altogether in a bachelor tank, and keep females spread out over several community breeding tanks. This uses the fewest tanks, and is effective if you are breeding for a specific, singular look. You remove males as they develop gonopodiums, and when the females stop having fry, take your best looking male(s) and add them into the tank. You can take a picture of the males you put in, and see how many of the offspring breed true. This is also a good way to test a single male at a time: throw him in with females who haven't had fry in 3 months, and see if he breeds true/breeds closer to the phenotype you are aiming for. After 3 months, separate males from females again, and keep pulling male fry until you go 3 months with no fry, then breed a bachelor in again.

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  • 2 weeks later...

Keep in mind that this is only necessary if you're breeding the same fish for many years.
Guppies are hardy fish. Most people will get bored with a strain before they ever have to worry about genetic issues.


Long-term you solve the problem by maintaining two lines.

Keep the two lines separate. All breeding happens within each line.
Each generation you're doing your normal culling and selection.
You want to select for different traits in each line. Often breeders will maintain one line for size, and another line for color and fin shape.
The point is that for each line your selection criteria is slightly different.

After 4 generations, cross the line. (a male from one line and a female from the other line)
Use the fish from this breeding to work into each of your lines (based on your selection criteria for each).

Continue breeding the two lines separately for the next three generations.

Then do another cross breeding.

Etc. etc. keep doing the same routine.
Keep the lines separate for 3 generations, then do a cross on the 4th generation.

This is how you would maintain/correct a strain in line-breeding.
If you're community-breeding, you can do something similar by keeping two separate communities. Estimate when you're about at the third generation, then cross-breed the 2 groups.

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