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How do people keep their breeding populations of fish healthy?

It seems common that people buy a group of one species of fish, from one source, which then breed. It's a fair bet that fish acquired this way would be from the same spawning, at what point does this become unhealthy? I read a comment somewhere to the effect that fish can interbreed for 11 generations without problems but that doesn't seem the best situation. However it's not necessarily easy to get unrelated fish.

How much do breeders worry about this kind of thing?

Generally speaking, it depends on the species.

Once I line-bred Ancistrus. Each year a new generation, but the third generation I bred (obviously, the parents could have been inbred as well) did not grow larger then 6 cm

But I also read some species/populations of life-bearers are actually so far inbred, they are genetically virtually indistinguishable.

What does inbreeding do? Basically it concentrates the genes - or better put, the alleles. A gene is the place where a protein's blueprint is kept, an allel is a version of the blueprint. Each animal has 2 varieties for each gene, one from mother, one from dad. If one of them is incorrect, the other can take over, and nothing happens.

But when in such a case brother and sister produce offspring, chances are the wring alleles meet - and in such a case no backup is available. Albinism is an example of what can happen, lack of growth another. But if the protein, and thus the allel is vital, such as in case of a gene for hemoglobulin, the red stuff in blood transporting the oxygen, the result is, obviously, death.

Therefore, the species the most vulnerable for inbreeding are the species which have the most genetic errors in their alleles. A wide spread species, which further exists as 1 population, such as the wildebeest on the African savannah are a good example. A species with a very small area, or with a lot of populations - such as many sweet water fishes, which do not easily jump from river to river, is an example of a species which can not afford to have much errors in the alleles - because such an error could easily take over the whole population, and make it then extinct.

From the above, one could assume inbreeding fishes - which can not have many errors - should be better possible than with mammals.

But there is another thing, our immune system is also passed on this way. That is, it is better to have say 50 varieties of a certain thing than 30 - because variety 45 could be why I survive a certain bacteria. Heavily inbred populations have less varieties in their immune system, and arte therefore more vulnerable.

Back to your question, I'm afraid most breeders do not pay enough attention to inbreeding. Or better put, I hope I'm wrong assuming most breeders do not pay any attention to inbreeding

Well said, Bas Pels. Inbreeding isn't automatically bad, but it does have negative side effects for most species over generations.

Mr Whippy, how do you intend to breed your fish? Do you just plan to breed the same parents over and over, or do you plan to take their kids and let the kids breed with each other? If you just have a set of parents and repeatedly breed those same parents together, that's not the same thing as inbreeding. Myself, I'm not a high volume breeder, but I have been breeding corys and banjos for about 3 years now. I started with a certain number of adults which I purposefully bought at different stores and which I use now as breeders; I trade or sell 100% of my offspring. Since I don't keep any offspring, they can't breed with each other, and thus no inbreeding occurs.

But my adults will eventually get old, so I've made it a habit after a couple of years to look for the same species of fish when I travel to different states and towns. I'll buy just one or two new fish, young adults, of the same species to add to my current parental breeding stock. Of course we can't know the parentage of the fish we buy in most stores, but by shopping at a variety of sources, I'm hoping that I'm raising the genetic diversity of my spawning groups.

I was going to start a line-breeding project recently, using an all-white albino BN female and a yellow albino BN male; this would have required two generations of inbreeding to set up. But alas just yesterday my female was found dead in the male's cave, her abdomen torn open. I'm wondering if the male was too aggressive with her during a spawning attempt.

Cheers, Eric

Thank you very much to both of you for your replies! Lots of useful information there.

Eric: Like many people, I bought fish and they bred and that has got me really interested in breeding. I have three sturisoma festivum which came from the same place at the same time and so are certainly related. They have bred and produced the most beautiful offspring the oldest of which are now breeding age themselves. I am trying to find some more so that I can make sure they breed to unrelated fish. The parents and offspring are in separate tanks so they will not be interbreeding. I love these fish and want to breed so that I can make sure I always have some. The original three are two males and one female and are roughly 8 years old now.

Luckily, the two farlowella vittata I have I am sure (as much as you can be anyway) are unrelated and they have bred a couple of times. I am hoping to acquire some from a new source to breed with the offspring. For the same purpose of been able to maintain a group for myself but also I would like any that I sell to be genetically healthy fish.

I have a group of Corydoras Habrosus who are breeding, I buy a few when I see them and add them in and hope this is enough to keep them healthy. I haven't done anything about rearing any fry, occasionally I notice the group has a couple of youngsters with them.

I have three Corydoras bought as Black Venezuelan's. They have just bred for the first time. I really want to carry on breeding these. The only place I know of that I can get any more is the same place the originals came from so I would not be confident that any others would be unrelated. I have exactly the same situation with Red Lizard Whiptails (L010a).

Sounds like you're having some good success with your fish. Congratulations.

In my opinion, if you're not trying to breed them in high numbers (I.e., like for commercial production), then the beauty is that your original parents should be productive for a few years (depending on species and their age when you acquired them). So that should allow you some time to find the occasional new individual to "refresh" your breeding stock, if you want to use that strategy.

And as already stated, inbreeding may be undesirable (so avoid it if you can), but a little bit of it isn't immediately horrific either. So should your babies breed, just don't make a habit of it generation after generation.

Cheers, Eric