F1, F2, F3... SO confusing!

[Ltygress]

I've bred other animals, and they use the F-numbers too. But for everything out there *except* fish, the F numbers are used to designate out-crossing to another breed.

With fish, it seems people are using them to designate *their* breeding success. I've seen it on eBay, here, Facebook, etc. On eBay, they apparently say F1 Zebra plecos are the first offspring that breeder has produced. F2 seems to be indistinct - sometimes it means the second brood of fish they've had from that species, sometimes it means the second generation. F3 is the same - sometimes the third brood, sometimes the 3rd generation. On these forums, it seems to be the first generation. Sometimes it is a tank-bred version that the person just acquired. Sometimes it is a pair of wild-caught bred in the tank. It's just so confusing!

But everything stops at F3 in other animals, because that's generally considered "back to the original breed". For example, lionhead rabbit kits are F1 if one parent is a Lionhead and the other is, say, a Nigerian Dwarf breed. F2 means one parent is that 50/50, and the other is pure Lionhead. F3 means one parent is 75% Lionhead, and the other is purebred. The next generation crossed back to a Lionhead, is considered pure Lionhead again, so there is no F4.

Generally these numbers are used to designate the cross-breed status so no one gets any high expectations about how they will turn out as adults. F1 may end up with the least desirable traits from both breeds as an adult, even though the final outcome is to get rid of those traits. F2 has a lower chance to look like both breeds. F3 is even less. And after that you *should* have achieved what you want from the out-crossed breeding when you get back to the original breed.

But in Fish, it seems F1 is just your first attempt at breeding... anything? Pure, hybrid, or whatever, it seems people are using it just to say "this is the first time I have bred these fish together". But really, the F designator doesn't matter with fish anyway. There are no "breeds" of fish yet, only species. And it doesn't matter beyond saying "tank bred" or "wild caught" either.

So I guess my question is, why is it used for fish at all? What is the purpose? And who came up with the idea of using them for all of these reasons? Why are others still insisting on using them when it has SO many different meanings? That just leaves you having to explain what *yours* are all over again, without using the designator anyway.

[bekateen]

Very interesting observations and question - what you're really seeing is not different appropriate uses of the F1, F2, etc., terms, but people using the terms incorrectly to suite their own purposes.

In fish as with rabbits as with birds, etc., there is a technically correct usage for the terms, and it has to do with generations of fry (F1) produced from a single set of parents (designated P or some people use F0), then the fry (F2) of their offspring, then the offspring after (F3), etc. It is always applied to crosses, although the crosses can start with two wild-caught parents of the same species, or with two captive raised parents of the same species, or of different species, or of different lineages such as color morphs (whether the lineages are wild-type or color morphs).

An accurate explanation is presented in this Shane's World article: Wild caught or captive bred?

Why do people tend to stop reporting around F3? I suspect it's not because they intentionally back to the original stock, but rather if they're selling F4, F5, F6, etc., fry, it leaves the buyer with a somewhat undesirable impression that the babies they're buying are inbred. Thus, as explained in the Shane's World article, if you have an inbred generation and you cross it back to a parent from a different (unrelated) lineage, or to a wild-caught parent, then you are starting over with a new F1 generation. Nobody I know wants to buy fish labeled F6, let alone even F3 in some cases.

Cheers, Eric

[Ltygress]

It is always applied to crosses, although the crosses can start with two wild-caught parents of the same species

This is actually one I don't agree with in any form. There is no way to know if the wild-caught parents are from the same lineage or not. Not all fish are migratory, meaning they will make their home right around the same location where they are hatched. The chances of breeding with their own parent or brother/sister is very high. So the first generation you get could actually already be F3.

[Bas Pels]

It is always applied to crosses, although the crosses can start with two wild-caught parents of the same species

This is actually one I don't agree with in any form. There is no way to know if the wild-caught parents are from the same lineage or not. Not all fish are migratory, meaning they will make their home right around the same location where they are hatched. The chances of breeding with their own parent or brother/sister is very high. So the first generation you get could actually already be F3.

Although theoretically this is possible, chances of this actually hapening are very slim indeed.

Assume a lake, surface a square mile. A few thousand fish of any species less then a foot long will live there, but the population will not increase. After all, the population is as big as possible.

Breeding will just replace the lder generations which are gone. That is, a breeding female will have room to prduce, on average, one breeding daughter.

Now, it could be a female is very succesfull, and will produce 2 or even 3 breeding daughters. And obviously also a few breeding males. That is, 3 in a population of thousands

Chansces of them meeting each other? Slim.

To me, F1 is the first generation bred from wild caught fish. F2 wil be their offspring

If one would breed F4 with a wild caught mate, to me calling the offspring F3 would be acceptable, but I think most people would call it F5

[Ltygress]

So that just goes right back to the original problem. Everyone uses it for different things, and that makes it confusing, and pretty much useless to use F designators!

[bekateen]

This is actually one I don't agree with in any form. There is no way to know if the wild-caught parents are from the same lineage or not. Not all fish are migratory, meaning they will make their home right around the same location where they are hatched. The chances of breeding with their own parent or brother/sister is very high. So the first generation you get could actually already be F3.

Although theoretically this is possible, chances of this actually hapening are very slim indeed.

Assume a lake, surface a square mile. A few thousand fish of any species less then a foot long will live there, but the population will not increase. After all, the population is as big as possible.

Breeding will just replace the lder generations which are gone. That is, a breeding female will have room to prduce, on average, one breeding daughter.

Now, it could be a female is very succesfull, and will produce 2 or even 3 breeding daughters. And obviously also a few breeding males. That is, 3 in a population of thousands

Chansces of them meeting each other? Slim.

For the reasons described by Bas Pels, I agree that unless you are working with a very small population of individuals in a small confined geographic area, with very limited access to other populations of the same species (and it's therefore a "founder effect" situation), then your odds of mating with full siblings is trivial in most natural settings; you might mate with cousins, but even that chance is reasonably low.

To me, F1 is the first generation bred from wild caught fish. F2 wil be their offspring

If one would breed F4 with a wild caught mate, to me calling the offspring F3 would be acceptable, but I think most people would call it F5

So that just goes right back to the original problem. Everyone uses it for different things, and that makes it confusing, and pretty much useless to use F designators!

Again, the P, F1, F2,... sequences have specific meanings scientifically. When two unrelated individuals are brought together for a first breeding, they are designated as "Parents" (P or F0) and their fry F1. All spawnings between full sibs of each subsequent generation are F2, F3, F4, etc....

But then to breed a wild-caught male with a captive-bred F4 female creates a new line, and the progeny would be a new F1. By "new line" I mean this F1 cohort cannot be equated back to the original F1 cohort created by the original parents who gave rise to lineage yielding the captive-bred F4 female that was used in the spawn at the start of this paragraph.

That the new babies should be considered F1 (vs a backward step from F4 to F3 or forward to F5) is especially true if the species is diploid. That said, if your species is polyploid, the genetic diversity in this new F1 will not be expected to be as diverse as would be the case for an F1 generation created from two wild-caught parents.

The F steps represent progressive levels of inbreeding. The moment you bring in a parent of a different source (i.e., not a full sib of the other parent), you break the inbreeding line. Again, please refer back to the Shane's World article: Wild caught or captive bred?.

Cheers, Eric

[TwoTankAmin]

I tend to agree with the above. But I tend to broaden this a bit because I do not spawn my fish in pairs but in small groups. Over time who is spawning with whom is impossible to determine. However, I will move offspring out of breeding tanks to grow tanks before that are able to spawn. If do not rehome them all, I end up with a small group of F1 fish from the group. If these fish go on to spawn I consider them to be F2.

If we think about this stuff for a bit it starts to seem a little silly to tighten the definition down to need the same two individual parents only. Consider nature and all its uncertainties. What are the odds that in the wild there is ever such a thing as an F2 fish? Even with fish that tend to pair for life, what are the odds that many months or years down the road (whatever time it takes for offspring to go onto to spawn themselves) will then fish a mate who is a true brother or sister. But let's supposes this happens. This has to repeat to get an F2 etc.

It seems to me that the more offspring produced in a given spawn, the lower the odds are of creating a true series of Fs. Nature has it way of insuring species will survive. One technique if to produce tons of eggs because many get eaten or because the small fry will be lunch. So the actual survivors of a single spawn my be so few that they will more easily find a mate who is not a sibling. Nature is more inclined to foster genetic diversity than inbreeding.

In my group of 10 wild caught L173. I know for sure two males do most of the spawning, but I think occasionally a third does. My best guess is more than one female is involved as well, but I cannot say for sure. Fms have a pecking order just like the males. However, I consider all of the kids to be F1. However, some are siblings, some are cousins and some may be completely unrelated. What all of them are is first generation from wild parents.

[bekateen]

I tend to agree with the above. But I tend to broaden this a bit because I do not spawn my fish in pairs but in small groups. Over time who is spawning with whom is impossible to determine. However, I will move offspring out of breeding tanks to grow tanks before that are able to spawn. If do not rehome them all, I end up with a small group of F1 fish from the group. If these fish go on to spawn I consider them to be F2.

In my group of 10 wild caught L173. I know for sure two males do most of the spawning, but I think occasionally a third does. My best guess is more than one female is involved as well, but I cannot say for sure. Fms have a pecking order just like the males. However, I consider all of the kids to be F1. However, some are siblings, some are cousins and some may be completely unrelated. What all of them are is first generation from wild parents.

I appreciate the difficulty of establishing parenthood when you have fish breeding in groups. For that purpose, people sometimes do simplify the term P/F0 to be a group of all-wild-caught parents, and then all of the fry, regardless of whom the parents were, are considered F1. And if you allow two of those babies to breed, they would be considered F2, and so on. If anything, in this case you are treating them conservatively because you'd be cautioning the buyer that these babies may be F2, although in fact, if the F1 fish that spawned to create the F2 were not related, then technically the "F2" would still be an F1 generation (but not F1 sibs of the original F1). What I'm saying is that such a collective usage does not violate the principle of the P-F1-F2 terminology because it's potentially over-estimating the level of inbreeding, instead of trying to mask more severe inbreeding.

If we think about this stuff for a bit it starts to seem a little silly to tighten the definition down to need the same two individual parents only. Consider nature and all its uncertainties. What are the odds that in the wild there is ever such a thing as an F2 fish? Even with fish that tend to pair for life, what are the odds that many months or years down the road (whatever time it takes for offspring to go onto to spawn themselves) will then fish a mate who is a true brother or sister. But let's supposes this happens. This has to repeat to get an F2 etc.

Let's keep the P-F1-F2 nomenclature in perspective. The terms were developed in the context of selective breeding by humans. While the concepts would still apply to natural populations, as you point out in most natural populations the concern is irrelevant and it is likely a waste of time to imagine it. That's why I treat all wild-caught fish as P fish, rather than even worrying about the likelihood that they might be F1 or F2 already.

Cheers, Eric