The attitude that "breeders must outcross", is so prevalent that I almost have to discourage it with most aquarists. However, there are times that it becomes absolutely necessary in order to save a line. Many don't understand why one should outcross vs. inbreed or even start over with a new line. Even proper outcrosses can sometimes cause many years of work to get a line back to where you want it. It is often simply much easier to start over with a better line. The key is to learn what will be most productive when trying to improve your line.
There are two main reasons to outcross. One is to boost the immune system and the other is to introduce genes that do not exist in your current line of fish. Waiting for the right mutation to come along is painfully slow (maybe hundreds of years, or longer). Therefore, find an unrelated fish that exhibits the desirable trait and breed it into your line. It doesn't matter if it's the same strain. In fact, sometimes it helps if it isn't the same. Simple, right? Well, not quite. Whenever you outcross, you not only risk bringing in undesirable genes, but almost certainly will. Some of these may be recessive and may not exhibit the unwanted trait for a few generations or longer. Even if you don't bring in any undesirable traits, you will loose the expression of any desirable traits that are the result of recessive genes your line contained before the outcross. Your orange Koi will likely no longer be as orange. The perfect body shape your line use to have, may not be so great. The pairs may not lay as many eggs, etc. You can get those traits back, but it will require more generations of inbreeding to do so.
Whenever you outcross, you can usually plan on needing a minimum of a few generations of careful inbreeding to accumulate undesirable recessives so you can eliminate them. In addition you have to work on accumulating homozygous pairs of all recessive genes that are desirable, so they will express the trait. Outcrosses can leave you with even more work than inbreeding and will most likely take much longer to see the results you want. The more ornate your strain is, the more an outcross will disrupt the expression of those traits. In the hands of the wrong breeder, an outcross or too many outcrosses can degrade the look of an ornamental beyond recognition. The outcross may introduce health and vigor, but it will likely degrade the ornamental appearance of the current line.
The most important outcross: If your line has many problems you have to decide if it would simply be easier or more productive to start with a new line. This is often the best decision. However, there are times when you absolutely must keep your existing line going. Usually this is when it contains a desirable trait that cannot be easily added to the line from another source. In this case, in order to preserve that trait you must outcross. Whenever confronted with a line that I must keep, but one that needs a lot of work, I almost always resort to an outcross with wild fish. Wild fish do have varying genetics, but nature has made them far stronger with more consistent positive traits than our man-made ornamental lines. The chance of introducing unwanted recessives when using wild fish is very low. This is another good reason to use wild fish. Getting wild fish to breed with our domestics, is a challenge all it's own, but that's another subject altogether.
After the outcross, it can take three or more generations of inbreeding to accumulate all the desirable recessives of the ornamental line we are trying to preserve. In addition, when using wild fish, the time it takes to produce each generation is usually extended (it's difficult to get wild fish to breed with your ornamentals). I've had projects like this take 10 years and longer, but even the first generation of the wild/domestic cross is usually a substantial and immediate improvement in many areas, like body shape, finnage, vigor and behavior. The results have always made it worth the time.
Next time I will write about line-breeding and its usefulness to the ornamental fish breeder.
Enjoy your fish,
© 2005 Angels Plus