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Inbreeding, good or bad?
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Furious George

PostPosted: 2003.05.06(Tue)14:17    Post subject: Inbreeding, good or bad? Reply with quote

I've seen reports, and accounts on the net that both promote and frown on inbreeding.
I have one generation of Molly fry, that are reaching maturity, should I think of adding some new genes into the gene pool?

Some have sworn by it- tha inbreeding enhances genetic purity, and although creates more indivuduals of a weak phenotype, it also creates a proportion of hardier individuals.

May I have your opinions and experiences?
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Joined: 05 Feb 2003
Location: Boston, MA, USA

PostPosted: 2003.05.06(Tue)14:33    Post subject: Reply with quote

Furious George, inbreeding can be good or bad, depending on what you want to achieve.

If you want to create new lines of fish that carry certain traits like color, tail shape, size, ... inbreeding becomes nearly inevitable. Only by inbreeding can you achieve a strain that faithfully reproduces the same traits as the parent generation.

Unfortunately, many genetic defects can emerge during inbreeding. Often, genetic defects are recessive, that means, it only emerges if you inherit the defect from both your parents. By inbreeding the chances of this happening are greatly increased, since the parents are closely related and probably carry a number of identical, recessive genetic defects. In addition, diversity seems to be very important for a functional immune system.

So, for healthy fish, do not inbreed. For fish with specific traits that you want, do inbreed. I hope this helps... mario
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The Old Salt

Joined: 01 Apr 2003
Location: Alabama

PostPosted: 2003.05.06(Tue)14:51    Post subject: Reply with quote

Those black mollies of yours are the direct result of inbreeding & linebreeding. Those fancy guppies in the petshop are, too. So are goldfish.

Selective breeding has been used for centuries to bend the phenotypes to our will. However, as you noted, the results are not always good.

As for defects, those fish with defects are removed from the program, allowing the work to continue with healthier fish, at least in theory.

The finished product is genetically limited, but pure. Sometimes this is a good thing, sometimes it isn't. It is true that a lot of the manmade strains of fish won't survive well in nature, and if allowed to breed in an uncontrolled fashion, the wild type traits will often return with a very few generations.

Now, as for your black mollies:
Black mollies have been black for a long time, and most of them are the descendants of a very few produced over 70 years ago. If you were to add more specimens to your little group, the odds are good that you wouldn't be adding any significant genetic diversity whatsoever. That said, you should probably add some anyway, but they'll be fine if you don't.

Hmm...I just now noticed that you didn't say these mollies were black. Whoops. If they're not, then get some more for sure.
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Furious George

PostPosted: 2003.05.07(Wed)12:48    Post subject: Thank You Reply with quote

My object is not to overpopulate my tank, I'd rather have a few good fry, as opposed to large school, so I believe I'll take your advice and inbreed (carefully, of course)

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Joined: 05 Feb 2003
Location: Raisinville, MI, USA

PostPosted: 2003.05.07(Wed)17:56    Post subject: Reply with quote

It depends on your goals. As pointed out, sometimes genetic defects aren't obvious, then after a few generations of inbreeding they become exaggerated.
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