I would have to disagree that hybrids are limited to the size of their parental species as far as being an intermediate of the parents (size being used arbitrarily.. Could be any trait of interest one is selecting for).

With hybrid vigor you basically experience a "greater" than the average (what you would expect) in gains for the attribute of interest. Not all crosses are good crosses tho.

The problem with hybrids is just that... Well, they are hybrids.

In order to retain 100% of the benefits of hybrid vigor (heterosis), you would have to be 100% sure that the pure strain of species A mates with the pure strain of species B every single time.

This basically means that you would have to maintain two populations of purebred species just so that you can get a consistent hybrid offspring every time. Otherwise you actually would over subsequent generations run into out-breeding depression, which could ultimately lead to the animals being the "average" of the parentals, which wouldn't be useful at all.

So it isn't the hybrid that will be the average of the two species / populations bred. It will be the "mutts" that result from the progeny of those hybrids which will average things out.

Hybrid = crossing two pure breeds

Hybrid X Hybrid cross, or Hybrid X Pure Strain Cross = Large Majority Mutts / Mixed individuals, and Low amount of truly Hybrid Individuals.

If you allow hybrids to mate with purebred species B, or A, or another hybrid, then the product will very likely not be what you were expecting, and you will not see the full benefits of heterosis.

That kind of makes the whole having hybrids thing pointless if you aren't carefully managing and selecting which individuals are going to mate with one another. Seems like more trouble than it is worth to me?

P.S.

I am sure that hybrids have their role in pond management, but I am not aware of the sex linked or sex limited traits that may prove beneficial. I don't claim to know anything when it comes to fishes. I am more of a production / companion animal kind of guy when it comes to genomics and animal breeding strategies.

Dr. Flores D.V.M.