A Zebra of a Different Color
Not all colors identified as Pseudotropheus zebra are what they seem.
There is a group of very attractive East African cichlids from Lake Malawi known to cichlid enthusiasts as the mbuna (pronounced um-boo-nah). Mbuna is the native name for these fishes, which translates as "rock-fish," referring to their preferred habitat, the rocky shores of the lake. Included among the mbuna is the species Pseudotropheus zebra.
Experienced African cichlid fish hobbyists are well aware of the controversy concerning cross-breeding of species. We're all against it, right? After all, wasn't nature generous enough? Consider, for instance, all of the "color morphs" of P. zebra that are available. We have BB (blue-black), cobalt, powder-blue, orange, white and albino — plus OB (orange blotch), red-top, black-top and red. Why cross-breed? Besides, new morphs are showing up every year.
Things are not that simple, however. Those familiar with the scientific literature know that ichthyologists specializing in Malawi cichlid fish would consider the morphs listed above to represent at least three, and possibly as many as five, distinct species. How, then, did the common belief arise that these morphs are all color varieties of one species, Pseudotropheus zebra?
The answer is the result of the popularization of the traditional view of speciation, to the exclusion more modern interpretations. In the past, species were defined on the basis of absolute genetic reproductive isolation (nonviable interspecific mating) and gross differences in anatomy. This traditional perspective of speciation has been altered considerably.
More recent studies have shown that in a natural environment, fish species can also be separated by behavioral reproductive isolation, the result of ecological specialization and/or geographic isolation. Genetic separation need not be absolute. What this ultimately comes down to is whether two populations in a true "free choice" situation will interbreed. If they do not, then they constitute two different species. Some of the morphs listed above are found in the same locations in Lake Malawi where the true P. zebra are also found, yet they do not cross-breed.
Let's examine why the traditional methods of identification of species fail when applied to mbuna. The first thing that strikes a newcomer to the mbuna is the significant anatomical similarity of these cichlid fish. It is difficult to identify different species by body shape. They share a generalized "torpedo" shape that is apparently marvelously adapted for life among the rocks in the shallows of the lake. Mbuna species differ from one another primarily in their specialized heads and in their behavior patterns.
Their heads allow physical access to, and their behavior causes orientation toward, very specific ecological niches in the nutrient-rich rocky zones of the lake. These niches consist of a limited range of depths, current conditions and types and sizes of substrate frequented by these species. The limits of the niches give rise to the aggressive, territorial behavior for which mbuna are so well known. Sometimes the niche includes strict specialization in diet as well, but more often extreme specialization in the types of fish food eaten is not characteristic of mbuna. More distinctive is where and how the different species feed.
The traditional method of using dead specimens for identification will not reveal information such as the size and location of territories or breeding behavior. It was only with underwater observation of mbuna communities that the extent of ecological specialization became evident. Such observation also revealed the lack of interbreeding among populations of physically similar species.
The more easily recognizable differences in anatomy do allow separation of groups of closely related species, known as "species complexes." These complexes are often seen listed in the popular aquarium literature as a single polymorphic species — however, many of these complexes are being assigned subgenus or genus status by Lake Malawi cichlid fish specialists.
Confusion concerning mbuna, and P. zebra in particular, also results from their polychromatic nature. For example, is it estimated that 3 percent of the females in the Cape Maclear population of P. zebra are orange with black spots (OB), and a much smaller percentage are orange with black eyes but no blotches (O). The vast majority of females are blue with faint black stripes (BB). Males are almost exclusively BB, with bolder black striping in the wild populations. (This may seem surprising considering the predominance of the OB morph in the hobby. Selective breeding by hobbyists has increased the occurrence of the OB trait.)
This variation in the Cape Maclear population is especially significant because of the historical precedence of this area in the origin of fishes in both scientific and aquarium collections. Because P. zebra far outnumbers other members of its complex in these early fish collection areas, the conclusion at the time was that there were numerous color variations of the species that were widely distributed in the lake.
Some species in the P. zebra complex are monochromatic, but usually do exhibit some form of sexual dichromaticism (males and females have different coloration). There is currently no explanation for this sexual dimorphism among monochromatic species. Different patterns may mean different species, but this can only be determined after associating the correct combinations of males and females.
Another factor that helped create the original confusion of species is the essentially unique sedentary nature of the mbuna. These species have been shown to be extremely reluctant to cross even short stretches of sand separating adjacent areas of the rocky habitats to which they are so well adapted. This factor promotes geographic isolation over what would otherwise be considered very short distances. Consequently, mbuna species are not usually widely distributed, but rather are endemic to their specific location in the lake. This is why location names are often included in the trade names for mbuna. These names, which are sometimes mistaken for scientific names, are well intentioned efforts to uniquely identify fish that have not been scientifically described so that they won't be bred with similar but geographically different fish.
Which brings us to the problem of cross-breeding and how it relates to the accurate identification of species. In captivity, it is quite easy to cross-breed mbuna. Therefore, aquarium spawning of different morphs is not an indication as to whether two fish are of the same species.
I have observed a ripe female of an unknown Pseudotropheus species (deprived of an appropriate mate) establish a territory, lay eggs and pick them up in her mouth without the benefit of any male (or female) attention. An interested male fish of almost any species might have made great headway under these circumstances. Because species can be so closely related, the fry will be viable — and probably fertile — for at least a few generations of hybridization.
I am amazed by the number of times I have spoken to people in fish stores, at meetings and at fish shows and events who boast that they have been successful in cross-breeding "Haplochromis this" with "Pseudotropheus that." It really isn't too difficult to accomplish these matings. The real skill is in preventing them through proper identification of the fish and taking care to house them separately.
I never hear the fry from these cross-breedings described as attractive — "interesting"" seems to be the most enthusiastic comment I recall. Perhaps the worst aspect of this is that passing these hybrids on to unsuspecting individuals leads to increased confusion and potential disappointment in the hobby.
The OB morph, as noted earlier, is orange with black spots. Describing this fish as an "OB zebra" is completely ambiguous, because P. zebra is one of many mbuna species that exhibit such a color pattern. The advantage conferred by this pattern is not understood, but it must be very significant to have been expressed so many times. Each of the three species below has an "OB zebra" morph.
The true Pseudotropheus zebra (Boulenger 1899) is one of the most numerous and widely distributed of the mbuna fish. It is particularly common in areas where the rocks are medium to medium-small in size, usually at depths of 15 to 65 feet. There is considerable geographic variation in color. Besides the BB, OB and O morphs, there are what might be described as "red-top" and "black-top" individuals at West Reef and Zimbawe Island respectively. In addition, what appear to be species that are similar in appearance to P. zebra, but exhibit different feeding behavior and seem to represent species other than P. zebra, have also been observed. The best information available is that the "albino zebra" available in the hobby was derived from the true P. zebra.
As of this writing, the "red zebra" is an undescribed Pseudotropheus species originating in the lake waters of Mozambique. Nowhere in its range does it coexist with the true P. zebra. Sexual dimorphism reaches a peak here, with the females of this species being red-orange and the males being the so-called "powder blue" zebras!
Obviously, color in this species is normally sex-linked. However, red male "red zebra" sports exist, similar to a male OB P. zebra. In this case, females reds crossed with male reds result in mostly red fry. There is also an OB female red zebra.
A morph described as an "albino red OB zebra" that became available raised the question as to whether this was an albino mutation that showed up in red zebras or the result of cross-breeding. If the latter, the fish would be ineligible for sanctioned exhibitions. Where had this albino trait come from?
It turned out that a Florida fish farmer who was preparing an order of red zebras from the grow-out pools — separating powder blue males from red males and females — realized that one of the fish, a female, was different. She was missing the normal black coloration around the eyes (albinos do not have melanin, the black pigment, in their skin). He found several more fish with the same trait, which were then spawned with a "Mozambique big block (OB) red" male. The albino mutation seems to be the spontaneous result of inbreeding a group of red zebras.
In the early days of the so-called "rift lake revolution," when mbuna were the hottest thing in the hobby, it was common wisdom that females of the "cobalt morph" were rare. It was suspected that the exporters of these cichlid fish were holding back females to ensure a monopoly. Supposedly, a similar but strangely different strategy was being practiced by the exporters of "white zebras." In this case, it was believed that the males were being held back.
The truth of the matter is that the cobalt zebra and white zebra are the normal female and male morphs of an undescribed species of Pseudotropheus zebra complex. "White" males and "cobalt" females are rare sports in the wild populations.
One researcher observed this species, which was referred to as P. zebra "cobalt," in distinct populations in the presence of the true P. zebra in four locations. They do not interbreed in a free-choice situation. These cobalts stay in shallower water, 10 to 35 feet deep, than do P. zebra.
Females of "cobalt zebra" are fairly common in the hobby, having been produced by breeding them with normal cobalt males. The "white zebra" has never become established in the hobby.
The clear and present danger in all of this is that the mbuna may go the way of the guppy fish. That is, because of the hardy constitution and ease of breeding these cichlid fish, combined with the low level of popular understanding of their taxonomy, there is the significant threat that any and all crosses within a species complex will be tolerated. Even worse, breeders will be encouraged to bring new morphs to the hobby. Every effort needs to be made to avoid this happening. Some dealers have aquariums of assorted African cichlid fish, none of which are identified, or perhaps even identifiable. Remember, a zebra of a different color most often isn't a zebra at all.