Can inbreeding affect size?

[daphnep]

Hello!

I have a large and happy group of aeneus in my 75 gallon. Most of them have been born in the tank. I never went into breeding seriously; it just sort of happened, and I did not think about swapping stock because I was just happy to see them happy.

Right now, there are four aeneus juveniles in a breeder's net, and I am waiting to set them loose with their parents and extended family, but there is an issue with size. One cory is growing well, and it will join the group in a week or so. The other three have not grown very well at all and are over half the size of their sibling. All are swimming, eating, and active as can be; they are healthy in every other way other than the three whose size is an issue.

I am considering putting the small three in a five-gallon tank that has different species of pygmy corys and a few miniature tetras, as they may be permanently tiny or grow at a very slow rate.

Has anyone experienced this type of breeding issue? And before you might suggest it, a supportive person has already sent me a new male and female, and I have an ad out to swap stock. If I cannot swap stock with a local person, I am going to buy some new females. To be honest, I did not expect my corys to be so prolific. Now I understand my part in all of this better.

Thank you!

[syno321]

The differing growth rates in spawns is fairly normal, and your smaller young aeneus will probably achieve normal adult size.

[Bas Pels]

When a student, quite a while ago, I was trying to inbreed my Ancistrus.

All went rather well, and in 3 years I had my third generation - which did not grow well, in any case much more slowly then their ancestors did, and certainly not breedable in a year.

More or less in that same tie, I came across an article on body size and heterozygoty in nature, it turned out the larger fish - juveniles - in a certain group were more heterozygote then the smaller ones.

In other words, the more diversity in the DNA, that is, the more alleles for a certain feature are available, the better the growth.

If one stops to think what it means, I think this is logically explainable. More allels for a certain feature implies that for instance the task is done in 2 ways instead of one, which can be the digestion of something. Having lightly different enzymes could mean the fish is able to get moreenergy out of the food, or for another feature, the fish can cope better with different temperatures, or can cope with more toxines in the environment.....

Whatever, the fish therefore tougher, and has a better chance of growing to the maximum its genes allow.

Whether inbreeding also reduces the maximums size is another matter - one I cannot answer

[rmc]

More or less in that same tie, I came across an article on body size and heterozygoty in nature, it turned out the larger fish - juveniles - in a certain group were more heterozygote then the smaller ones.

This being said - would it make sense with a limited population of a certain fish (i.e. chances of getting new wild stock for better blood lines are slim) to breed only the larger fry (ones that are more heterozygous)? To continue the captive population in the best way possible.

[Birger]

Another thing to consider is what is the size of wild fish compared to tank raised....often, as is the case with Malawi Cichlids for example, you often see fish much bigger then you would in the wild because of high protein diets etc.

So is it always wise to use the biggest fish or chose on size alone???

Birger

[bekateen]

In my limited experience with corys, banjo cats, and several cichlid species, I find that within a group of juveniles (all siblings hatched at about the same time), there will inevitably be one, or two, or maybe a few individuals, that accelerate ahead in growth, far ahead of all the other juvies. Once that happens, the larger juvies start growing really quickly, and the smaller juvies seem to have their growth stunted, even if the aquarium is nowhere close to being overcrowded. My solution is to remove the largest juveniles, and within a short time all the smaller juvies will start to grow again... until another one or two get too large, and then the process repeats. Ultimately, nearly all of the juveniles reach what you might consider normal adult size, with some variation, but it just takes the slowest growing individuals a really long time.

I've read before that larger fish secrete a "growth stunting" pheromone to suppress their siblings, and my observations are consistent with that. However, I've never been convinced that this is really the right explanation - it could also be that the largest juvies are simply hogging most of the food, leaving the smaller fish with less nutrition and slower growth; I've also read that smaller fish are more severely influenced by urinary wastes than are larger fish, so that too could stunt growth selectively, without per se being a pheromonal effect.

[NCE12940]

Article that might be of interest -
http://beheco.oxfordjournals.org/content/21/4/884.full

Many, many years ago a vet, Whitney, did inbreeding experiments with guppies and after a decline in viability they *recovered*. Unfortunately it's also been many, many years since I read about this and the book the info's in is buried in a pile of books. Long enough ago that I can't find anything on Google & can't remember Whitney's given name. He did many breeding experiments with dogs also.

[bekateen]

This being said - would it make sense with a limited population of a certain fish (i.e. chances of getting new wild stock for better blood lines are slim) to breed only the larger fry (ones that are more heterozygous)? To continue the captive population in the best way possible.

Regardless of the importance of the degree of heterozygosity or homozygosity (i.e., how diverse the genes are within a single fish), no matter what, it would seem wiser (genetically speaking) for health reasons to breed only the fastest growing of your fish. Barring a tumor that causes fast growth (think of giant humans, who sometimes have growth hormone tumors), faster growing individuals are considered more "robust" according to evolutionary biologists, often with stronger immune systems, or as mentioned in an earlier post, a higher tolerance of suboptimal water conditions. Of course there could be other underlying problems in these fish, but until you identify those, I think selecting faster growing fish is pretty safe.

I would however, reframe your proposal in this way: Instead of selectively breeding only the fastest growing fish, I would propose selectively NOT breeding the very slowest growing. That would allow the fish with intermediate growth rates to continue contributing to the population gene pool, and it would cull from the group any potential gene defects that cause overt stunting.

[bekateen]

Here is an article (Active Inbreeding in a Cichlid Fish and Its Adaptive Significance) that finds some level of inbreeding to be a good thing for the fish in this case, with no measurable negative effects on growth rate. But there are plenty of other articles that show, not surprisingly, inbreeding is bad.

[NCE12940]

I think that, without controlled breeding, it would be difficult to predict. You'd have to know a fair amount of background on the parents, particularly how closely related they themselves are, if at all. And information such as what their siblings and parents produced. Assuming the parents are not related or not closely related you're probably not going to get anything detrimental due to inbreeding. I suspect many in the *hobby* don't have this sort of information, making it more of a crapshoot. (It's a lot simpler in dogs where you don't have offspring in the 3 figures!)

[Corycory]

I have a group of hybrid corys whose parents are albino aeneus and gold lasers. They grew up with they pure albino siblings which hatched at the same time.
Two years down the road, the hybrids are way larger than any albino siblings and grew up way faster to start with. They are larger than any of their parents albino and gold lasers which I've had for years and the laser parents are smaller than the albino parents naturally.
They've all been fed the same food.

[NCE12940]

F1, hybred vigor. Probably won't happen with continued inbreeding (breed F1s back to parents or to siblings, do the same with the F2s, and so on.)

[Corycory]

I suppose you are right. I won't be breeding the hybrid(F1s) so I won't be seeing it for myself.

[Bas Pels]

Where do you think Hybrid vigor comes from?

I would assume it coming from combining lines which are very unrelated, and therefore the offspring is very heterozygote

hybridizing these fishes further might result in furthe vigor, espacially if one would perform the back-cross with fishes unrelatedto the parents

To summarize, I would consider the hybrid vigor as proof for the size affection inbreeding has

[NCE12940]

Where do you think Hybrid vigor comes from?

I would assume it coming from combining lines which are very unrelated, and therefore the offspring is very heterozygote

hybridizing these fishes further might result in furthe vigor, espacially if one would perform the back-cross with fishes unrelatedto the parents

To summarize, I would consider the hybrid vigor as proof for the size affection inbreeding has

Yes, but that usually is only going to work for the F1s. If you take the F1s and breed to unrelated fish you're no longer inbreeding, you're outcrossing. If you breed the F1s to siblings or parents you're going to start losing the characteristics you got with the F1s. This is the usual progression with intense inbreeding.

[bekateen]

I have a group of hybrid corys whose parents are albino aeneus and gold lasers.

Unless the two species are very closely related, interspecific hybridization opens a whole new can of worms, when compared to intraspecific hybridization. Does anybody know the chromosomal make up of either aeneus or gold lasers (CW010)? Depending on how the hybrids formed, this can affect whether or not the large size of the hybrids will disappear with subsequent F1 X F1 inbreeding (assuming the hybrids are fertile at all).

If aeneus and gold lasers have the same number of chromosomes, then your hybrids are probably homoploids (they have the same number of chromosomes as each of the parent species). In that case, then your interspecific hybrids are something close to the classic intraspecific heterozygous hybrid created by crossing two different strains of the same species, and their enhanced growth will likely disappear with subsequent F1 X F1 inbreeding.

However, if aeneus and gold lasers have a different number of chromosomes, then your hybrids could be polyploids (this could also be true, although much less likely, even if the aeneus and gold laser parents have the same number of chromosomes). If your hybrids are polyploids, then the enhanced growth may be a result of the polyploidy itself, rather than the heterozygosity, and in that case the growth rate will be fixed, i.e., it won't disappear in subsequent generations.

Having said that, among animals interspecific hybrids are often sterile (a phenomenon called "decreased hybrid fertility" -- it may seem counterintuitive given the enhanced vigorous growth, but just consider mules), or their fertility can decline over a couple of generations if they do successfully breed at first (a phenomenon known as "hybrid breakdown").

So unless someone tries to breed the aeneus X cw010 hybrids, you won't know whether or not their fertility is impaired.

P.S., Going back to the initial question about inbreeding affecting size, heterozygosity due to intraspecific matings may result in larger size (as several of the above posts demonstrate), but it shouldn't fundamentally impair fertility at all over generations (if anything, it may improve it; that can be part of "hybrid vigor"). That's opposite of what often occurs among the offspring of interspecific hybridizations (at least among animals; plants are a different story).

[apistomaster]

Rainbow Trout polyploids are infertile and tend to grow larger and faster. This may be because they are not diverting energies towards reproduction. I would not be surprised it the same wouldn't apply to a polypoid Cory.

I have the most experience with inbreeding lines of domestic Discus.
I never had any problems with subsequent generations not reaching their normal size.
With Discus spawns there are always some runts and some which outgrow most of their siblings.
This happens even when two wild and unrelated Discus breed together.

I suspect that improving feeding, space and water quality would eliminate the majority of the stunted fish you are seeing. This could be improved considerably with your greater experience. That being said, it never hurts to introduce new genes into the gene pool.
I guess I belong to the school of thought that says inbreeding fishes isn't as serious a problem as most other factors. Many modern strains of tropical fish across many different families has not resulted in significant size issues. I am not saying inbreeding is a best practice if there are other options or goals. However inbreeding is essential when attempting to "fix" a mutation which may have some commercial value.

[Bas Pels]

I guess I belong to the school of thought that says inbreeding fishes isn't as serious a problem as most other factors. Many modern strains of tropical fish across many different families has not resulted in significant size issues. I am not saying inbreeding is a best practice if there are other options or goals. However inbreeding is essential when attempting to "fix" a mutation which may have some commercial value.

If one would want to fix a mutation, inbreeding is what usually happens. Still, personally I would consider any albino as an error - that is I would cull the albino and certainly not breed with it. I'm not in the hobby for money. In fact I would prefer buying from breeders who do the same.

A better way to fix an mutation, however, would be to crossbreed the mutated fishes with unrelated fishes without the mutation - resulting in normal fishes - and inbreeding these. One quarter will have the mutation, but the fishes are rather unrelated, and thus genetically much healthier

If one would have 1 mutated fish, of an easy to breed species, with huge litters, one could crossbreed it with multiple unrelated mates, and keep the offspring separated.

As the offspring all carries the mutation, one could breed semi related offspring (only related in having the Original mutated fish as parent) with each other, resulting in mutated offspring in huge numbers, which are genetically healthy

One could even go further and do the same again with this offspring, for instance using new wild caught fishes.

But, alas, normally in such a case the breeder only uses 1 mate, multiple times.

[Corycory]

I haven't been around for a while.

So unless someone tries to breed the aeneus X cw010 hybrids, you won't know whether or not their fertility is impaired.

So they are living amongst themselves, unfortunately with a crowd of fish that eat eggs. But what you are sayig is that if I try to breed them I can figure out the puzzle...

[Corycory]

Having said that, among animals interspecific hybrids are often sterile (a phenomenon called "decreased hybrid fertility" -- it may seem counterintuitive given the enhanced vigorous growth, but just consider mules), or their fertility can decline over a couple of generations if they do successfully breed at first (a phenomenon known as "hybrid breakdown").

So unless someone tries to breed the aeneus X cw010 hybrids, you won't know whether or not their fertility is impaired.

Hey, it's been a while but I collected eggs from the said aeneus X cw010 hybrids. The eggs are viable and now I am waiting for them to hatch. Details will appear in my old thread below. I only picked up 4 eggs for experimental purposes. The mother is one of the "hybrids". However I don't know who fertilized the eggs, an albino aeneus or a male hybrid.

http://www.planetcatfish.com/forum/view ... 5&start=60