View Full Version : weak fish and genetics

11-28-2016, 07:26 PM
So, here's this female. She is S/S pb/pb, g/gm or gm/gm. This seems to add up to a genetic burden like hb/hb: She is small for an adult, and lays smaller eggs.

Here are a couple questions:

Which genes here are likely most responsible for this "genetic burden"?

Now imagine this: there's a female hb/hb and a male hb/+... when will the difference in vigor between the offspring show up?

What about the reverse situation: hb/+ female and hb/hb male. Will these offspring all get off to a better start since the female is likely laying larger eggs?

11-29-2016, 04:54 PM
I'm not aware of Half black having growth or survival issues, although they can be a challenge to get them to express the half black pattern. However not having bred them myself, I'm not categorically saying they don't have issues.

On a more general point, often the perceived problem of a particular gene being weak stems not from the gene itself but because it's recessive...

If for instance you wanted to breed blue angels, one approach might be to buy a blue angel and pair it with a totally unrelated fish, but you'd have no blue offspring. 9-12 months later you could take two of the offspring and pair them together, and you'd get just 25% blues. Or you could breed one of the offspring back to the original blue parent. Either way, it might be 18 months or so on from the start of the original project before you got your first blues. These fish are already 25% inbred compared to their parents, but you want to be breeding blues, not all the other colours produced so far, so the temptation is to pick a pair from this second generation to breed from.
By the third generation the level of inbreeding would already likely be having some impact on the size, growth and health of the resulting offspring, but probably not too substantial.
However now you've got your first generation of 100% blues, now would be a really great time to do an outcross, but who want's to go back to the start of this project at this stage?

Now you might argue that you don't have to start with one blue fish, you could buy several, but unless you shop around from several different breeders, and even then quiz them carefully about the origins of their breeding stock, there's a serious risk of starting with reasonably closely related individuals.

Once you start looking at fish with two or three recessive genes combined in the same fish, the temptation to push things for one too many generations can be very strong.

So whilst I would agree that blues do tend to be smaller and slower growing than "normal" angels, I don't think it's inevitable that all blues will be, some of my largest fish are blues.

In short, the problem is mostly not the "genetic burden" of the particular gene combination you know about, it's more down to the deleterious effects of, often inadvertent, inbreeding by which the fish were produced.

11-30-2016, 05:25 AM
Thanks for this detailed reply. Here's what experienced hb breeders have told me: The fry are not large enough to take bbs for several days, grow more slowly etc.

The more important points, and here I agree completely: Line-bred or inbred fish will become weaker with each generation. It is best to know and keep track of the genetics and relations of the fish you buy and the fish you breed. Healthy fish that are not closely related make the best parents.