Is inbreeding a problem?

[strobukm]

I have a 46 gallon bowfront tank of neolamprologus multifasciatus that has been running for about 5 years. I started with 8 fish from 2 different sources, now there are at least 50 adults. I’ve noticed that several of my fish have what appears to be facial deformities or possibly old injuries that healed weird, though I’ve never seen a fish with a visible injury. These deformities are mostly in non-dominant males. Can this be caused by inbreeding? The fish pictured swim and eat fine, but one of them looks like he can’t close his mouth, another has a weird shaped face, and another has a crooked mouth.

 

[TClare]

Facial deformities are certainly a frequent consequence of inbreeding in various mammals, including humans. I am not sure about fish, but it would not surprise me. Inbreeding also leads to reduced fertility, low offspring survival and increased vulnerability to disease (among other things) in most animals and plants that have been studied.

 

[A201]

The Cichlid with the gaping hole mouth looks to have survived mouth rot.
I've seen that same situation occasionally on fish at my local fish store. The mouth tissue destroyed by the bacteria does not regenerate, leaving a lip-less mouth.

 

[strobukm]

The Cichlid with the gaping hole mouth looks to have survived mouth rot.
I've seen that same situation occasionally on fish at my local fish store. The mouth tissue destroyed by the bacteria does not regenerate, leaving a lip-less mouth.

All three deformed fish pictured definitely have lips. The one with the gaping mouth, has a full set of lips, his mouth is just always open. He eats just fine by sucking food into his mouth. I can’t bring myself to euthanize fish just because they’re deformed, but maybe that’s what I should be doing. I doubt the deformed ones are breeding because they’ve been chased away from the females, who all have shells on the bottom of the tank, up onto the higher tiers of their little society. In this case, the higher you live, the lower you rank.

 

[TClare]

If it is inbreeding the addition of just one or two new individuals from a different line can dramatically help to reduce inbreeding depression (in this case the occurrence of deformed offspring). But I don’t know if any new fish would be tolerated by the others?

 

[GlennO]

How many generations since the original 8?

 

[strobukm]

How many generations since the original 8?

I’m not sure. I don’t ever separate fry and raise them, I leave them in the tank with the adults, most eventually get eaten, but enough survive that the 8 has turned into at least 50-60 adults. The original 8 were about 5 years ago though and a only a few adults have died over the years, maybe 3.

If it is inbreeding the addition of just one or two new individuals from a different line can dramatically help to reduce inbreeding depression (in this case the occurrence of deformed offspring). But I don’t know if any new fish would be tolerated by the others?

That’s a good idea. I can post locally and see if anyone is willing to sell me a few new females.

 

[GlennO]

I think once you've got siblings breeding amongst themselves for a couple of generations it's best to thin them out and add some new blood.

 

[LowConductivity]

I don't know that I'd say "inbreeding" is a problem per se. The problems are "selective breeding", and "forced pairings" IMO. Given a reasonable sized population of wild or f1’s to start with, I'd have little to no concern about a naturally selected brother/sister pairs (*key words there, naturally selected) generation after generation

 

[TClare]

With a reasonable sized wild or f1 population there are unlikely to be many issues related to inbreeding for several generations. But in a home aquarium the initial population is not often reasonably sized, but quite small and with repeated generations of brother sister matings issues related to inbreeding are almost inevitable, since genetic diversity is drastically reduced and the chances of two harmful recessive alleles coming together and being expressed are increased with each generation. This does not mean that all offspring will be affected, but the incidence of weakness, low survivability, deformities etc. is likely to increase. This is well known in almost all domestic animals and plants, as well as in small populations of endangered animals that have been drastically reduced by human activities such as hunting and habitat loss. It is a big problem in conservation because even if hunting is prevented and habitats are protected populations may not recover due to inbreeding depression and loss of genetic diversity, unless a few new individuals from another population are added (there are of course exceptions but I don't want to go into this in too much detail here).
Just to add to this, LowConductivity is certainly correct in that selective breeding will more quickly lead to inbreeding issues than natural pairing, since with selective breeding individuals are selected that share characteristics that the breeder wishes to fix (eg a particular colour or long fins etc.) and individuals which possess these characteristics are more likely to be similar to each other genetically than those who pair naturally hence genetic variation is reduced more quickly.

 

[chromedome52]

The mouth deformities are usually the result of overcrowding. It tends to affect the fry at a very young age, I've seen it in large spawns where I had to keep them in a confined space for too long. The fact is, actual genetic deformities are quite rare. Environmental conditions are far more likely to cause problems for growing young, especially when confined in aquaria.

 

[strobukm]

Thanks for all of the information! Based on all of your replies I've decided to rehome about half of my colony and add a few new ones to introduce some genetic diversity. I'll obviously keep the deformed ones and since they're all male, I may set up a smaller tank to keep them in to prevent them from breeding.

 

[MacZ]

I can’t bring myself to euthanize fish just because they’re deformed, but maybe that’s what I should be doing.

As a former long time breeder of Rift Lake cichlids: Yes, as sad as it seems, somebody has to take the role of population control.
Moving the surplus males to a tank of their own is a very good decision.

 

[ruud]

I don't know that I'd say "inbreeding" is a problem per se. The problems are "selective breeding", and "forced pairings" IMO. Given a reasonable sized population of wild or f1’s to start with, I'd have little to no concern about a naturally selected brother/sister pairs (*key words there, naturally selected) generation after generation

It depends on what you are after. Natural selection is of a different kind once we keep species in tanks and genetic drift plays a major role as well. You quickly end up with your own "ecotype".

Thanks for all of the information! Based on all of your replies I've decided to rehome about half of my colony and add a few new ones to introduce some genetic diversity. I'll obviously keep the deformed ones and since they're all male, I may set up a smaller tank to keep them in to prevent them from breeding.

Not to make it too complex, but outbreeding too can lead to reduced fitness to the point where the conventional definition of species becomes clear. But I don't wanna make it too complex for myself either, so I separate the male and female Dario's of the same generation to different tanks and sometimes introduce a specimen from outside whenever I get the chance, and that's really about it. And I too have a large tank where I keep Dario's that I not intentionally breed as I need a place for the surplus.