Chromedome
10-24-2007, 11:15 AM
I've been following this discussion, tried to stay out, but there are a couple of points that people don't seem to be aware of. As far as killing hybrids is concerned, I would prefer to see them fed to large predators, as that satisfies both the needs of the predator, and removes bad bloodlines in a manner consistent with nature. I cull my fish, even those that are not hybrids, as I wish to raise only the best quality. If you can't do this, then don't breed fish. There are already plenty of poor quality fish out there commercially, don't add to it.
Now as to new information: I've seen some mention of not mixing species of the same genus. With Malawian cichlids, it doesn't matter if they are different genera. They will interbreed, and produce viable hybrids. The vast majority of people who keep Mbuna don't seem to realize this, or don't believe it when you tell them so. The most extreme hybrid I've seen was a Dimidiochromis compressiceps with a Pseudotropheus livingstonei. And what happened to these fry? The guy sold them as "Haplochromis kalamazooi" (the town here in Michigan). This was over 25 years ago, but it soured me on Malawian Cichlids and the people who keep them for at least a decade and a half.
Personally, I don't care if you destroy the hybrids or keep them alive, but don't let them out of your personal control. And the next step should be to remove the risk of having it happen again. If you don't do that, you will continue to produce fish that could destroy a natural lineage.
Everyone needs to understand two things that are unique about the cichlid species flock of Lake Malawi:
1. The Lake is very recently (on a geological time scale) colonized. This means that the fish here haven't been speciating for very long.
2. It is believed that all the cichlids in Lake Malawi are descended from at most a handful of riverine species - some researchers believe it may have been just a single species. As a result, they are very closely related, and all breed in the same way, "advanced" mouthbrooding. This allows for easier hybridization, as there is little variation in the behavior.
The first point combined with the second means that the fish are still far too closely related to be genetically isolated. This is one of the reasons Malawian cichlids are a particular risk for accidental hybridization. They've developed extremely varied feeding behavior, but breeding has not yet become an isolating factor. In the wild, the feeding habits tend to keep them in apart. In aquaria, species are forced into closer proximity, allowing more opportunities for hybridization. Incidentally, many of the modifications for feeding aren't genetically based. Cichlids are extremely elastic. Fry from any given species can and do have different teeth from their wild parents in a single generation. This puts species descriptions based mostly on dentition in doubt.
They are also geographically isolated within the lake because of territoriality; they don't wander that far from their starting point and therefore have fewer opportunities to hybridize in the wild. In the wild, female Mbuna can seek out a dominant male of their own species, but in aquaria, they will spawn with a male of any species who is dominant in that tank, and most aquaria are not large enough to allow territory for more than one or two males, regardless of species. So either stop mixing multiple mbuna species, or start keeping aquaria with an extremely large footprint. 2'x8' is space for two, maybe three males of very small species. Think about that.
Hybridization as an engine of evolution: It has recently been proven that, yes, some species are the result of accidental hybridization. However, this is an extremely rare occurrence, and not the normal procedure. Geology often plays a large part in population isolation, and if they are isolated long enough, they can evolve into a genetically incompatible group from the original species. Adaptation to a new environment - this is the primary force in speciation in Lake Malawi - can produce behavioral isolation, even though genetically compatible individuals are living in close proximity. Eventually, the two lines may diverge genetically to the point of incompatibility. But most of the Cichlids in Lake Malawi are not there yet.
So when collectors moved a species of a highly desireable, but distantly located, Mbuna to a rock pile closer to the collection station, the fish sought out others with similar behavior. Females of a species that was already there found that they liked the looks of the new species' males better than their own, and started to hybridize. That was the beginning of the end for the indigenous species. However, females of the introduced species, as well as the other females, found that the new hybrid males were even more irresistable than the introduced males. End result, both of the original species are gone from that rock pile, and the hybrid is now filling the niche. If this had happened naturally we would probably call it a new species, but because man interfered, we do not.
Point being, getting Wild Fish is not the guarantee of purity that everyone seems to think it is. But allowing hybridization to continue in an environment under our control is not acceptable behavior for the fishkeeper, either.
Now as to new information: I've seen some mention of not mixing species of the same genus. With Malawian cichlids, it doesn't matter if they are different genera. They will interbreed, and produce viable hybrids. The vast majority of people who keep Mbuna don't seem to realize this, or don't believe it when you tell them so. The most extreme hybrid I've seen was a Dimidiochromis compressiceps with a Pseudotropheus livingstonei. And what happened to these fry? The guy sold them as "Haplochromis kalamazooi" (the town here in Michigan). This was over 25 years ago, but it soured me on Malawian Cichlids and the people who keep them for at least a decade and a half.
Personally, I don't care if you destroy the hybrids or keep them alive, but don't let them out of your personal control. And the next step should be to remove the risk of having it happen again. If you don't do that, you will continue to produce fish that could destroy a natural lineage.
Everyone needs to understand two things that are unique about the cichlid species flock of Lake Malawi:
1. The Lake is very recently (on a geological time scale) colonized. This means that the fish here haven't been speciating for very long.
2. It is believed that all the cichlids in Lake Malawi are descended from at most a handful of riverine species - some researchers believe it may have been just a single species. As a result, they are very closely related, and all breed in the same way, "advanced" mouthbrooding. This allows for easier hybridization, as there is little variation in the behavior.
The first point combined with the second means that the fish are still far too closely related to be genetically isolated. This is one of the reasons Malawian cichlids are a particular risk for accidental hybridization. They've developed extremely varied feeding behavior, but breeding has not yet become an isolating factor. In the wild, the feeding habits tend to keep them in apart. In aquaria, species are forced into closer proximity, allowing more opportunities for hybridization. Incidentally, many of the modifications for feeding aren't genetically based. Cichlids are extremely elastic. Fry from any given species can and do have different teeth from their wild parents in a single generation. This puts species descriptions based mostly on dentition in doubt.
They are also geographically isolated within the lake because of territoriality; they don't wander that far from their starting point and therefore have fewer opportunities to hybridize in the wild. In the wild, female Mbuna can seek out a dominant male of their own species, but in aquaria, they will spawn with a male of any species who is dominant in that tank, and most aquaria are not large enough to allow territory for more than one or two males, regardless of species. So either stop mixing multiple mbuna species, or start keeping aquaria with an extremely large footprint. 2'x8' is space for two, maybe three males of very small species. Think about that.
Hybridization as an engine of evolution: It has recently been proven that, yes, some species are the result of accidental hybridization. However, this is an extremely rare occurrence, and not the normal procedure. Geology often plays a large part in population isolation, and if they are isolated long enough, they can evolve into a genetically incompatible group from the original species. Adaptation to a new environment - this is the primary force in speciation in Lake Malawi - can produce behavioral isolation, even though genetically compatible individuals are living in close proximity. Eventually, the two lines may diverge genetically to the point of incompatibility. But most of the Cichlids in Lake Malawi are not there yet.
So when collectors moved a species of a highly desireable, but distantly located, Mbuna to a rock pile closer to the collection station, the fish sought out others with similar behavior. Females of a species that was already there found that they liked the looks of the new species' males better than their own, and started to hybridize. That was the beginning of the end for the indigenous species. However, females of the introduced species, as well as the other females, found that the new hybrid males were even more irresistable than the introduced males. End result, both of the original species are gone from that rock pile, and the hybrid is now filling the niche. If this had happened naturally we would probably call it a new species, but because man interfered, we do not.
Point being, getting Wild Fish is not the guarantee of purity that everyone seems to think it is. But allowing hybridization to continue in an environment under our control is not acceptable behavior for the fishkeeper, either.