Half a Century of Experience with Tropheus Species: A Summary, Part 1Author: Wolfgang Staeck
In 1958, exactly half a century ago, the first live cichlids from the genus Tropheus were imported as aquarium fish into Europe. A look back at the past 50 years provides not only insight into an interesting chapter of the history of the aquarium hobby, but also into the evolution of research techniques in ichthyology.
Although many interesting and colorful cichlids are regularly imported from Lake Tanganyika, hobbyists who specialize in these fish have always focused on the genus Tropheus. This is rather surprising, as the Tropheus species are not fishes recommended to inexperienced aquarists due to two main characteristics: extremely high aggression towards conspecific individuals, and their susceptibility to certain infections of the intestinal tract. As a result, slight mistakes in keeping them may immediately cause bitter disappointment. Tropheus species are also not cheap, but this seems to be a particular incentive for some hobbyists to buy these cichlids.
The first fishes from the genus Tropheus were sent to Europe at the end of the 19th Century. They were three dead specimens that Prof. J. E. S. Moore had caught for the British Museum in 1895 and 1896, which were then later used by ichthyologist G. A. Boulenger to publish the scientific description of Tropheus moorii in 1898. Half a century later in 1956, Max Poll published the first description of the colors of a live specimen. By the end of the 1950s, numerous isolated populations of Tropheus with different patterns of coloration were discovered in Lake Tanganyika. In 1959, Marlier distinguished between four color varieties—black, orange, yellow, and red. And in 1962, Matthes discovered five additional variants in the northern part of the lake.
From 1974 onwards, when a group of German aquarists first traveled to Kigoma in Tanzania, several ichthyological expeditions and the search for new aquarium fishes resulted in the discovery of numerous new color varieties. Early in 1975, another group of German aquarists went to the southern part of the lake to search for new Tanganyikan cichlids in Zambia. Their stay at Kasaba Bay in Sumbu National Park is an important date in the history of the exploration of the lake—in those days, they discovered numerous colorful cichlids endemic to Zambia, and among them were many attractive Tropheus populations that were previously unknown (Staeck, 1975). These discoveries prompted several importers of aquarium fish to bring them to Europe.
However, the first live specimens of a Tropheus population had already been imported to Germany in 1959 (Ladiges, 1959; Chlupaty, 1961). The owner of Aquarium Hamburg in Germany caught them in the vicinity of the village of Bemba, which is situated at the northwest coast of Lake Tanganyika in the Republic of the Congo. Since there was almost a complete lack of information on the peculiar ecological demands of these cichlids at the time, the fish quickly died out again in the hobby because of improper maintenance. The Tropheus population of this locality—known as “orange variety,” and used by Wickler (1963; 1965; 1969) for his ethological studies—is not a type of T. moorii according to recent discoveries, but a separate species.
Ten years passed before a Tropheus species was again imported to Europe. In 1971, Pierre Brichard (who originally had exported aquarium fish from the Congo, but moved to Burundi in the late 1960s) began to ship Tanganyikan cichlids; frequently among them was the Tropheus population occurring at Rutunga. In the next few years, some Tropheus from Kigoma (Staeck, 1974) and the first exports of the colorful populations from Zambia reached Germany, which triggered a real Tropheus boom.
Until the end of the 1980s, most of the Tropheus populations were regarded as geographical races or color morphs of T. moorii, but several recent scientific studies published since 1992 have concluded that this notion is not true. The analysis and comparison of mitochondrial DNA sequences of different Tropheus populations (Sturmbauer & Meyer, 1992; Baric et al., 2003; Sturmbauer et al., 2005) provided new approaches to a better understanding of the evolution of the Tropheus species and to a future taxonomic revision of the genus. The results of these genetic studies were that several lineages with distinct patterns of genetic divergences can be distinguished among the approximately 100 different colored populations, which originally were described as color morphs of T. moorii. Some of them have to be regarded as separate, undescribed species. In T. duboisi,the degree of its genetic divergence is so high that a new genus will probably be described for this species in the future (Sturmbauer et al., 2005).
However, up to now, all these findings had no consequences for the taxonomy of the genus Tropheus. In the hobby, the results of the genetic studies were reported (Schupke, 2003), but there were no consequences. Because of the very complex patterns of distribution of the different lineages and species, most aquarists usually continue to consider all Tropheus populations as mere color variants of T. moorii and distinguish between them by referring to their collecting sites.
Apart from T. moorii, taxonomists distinguish five additional species in the genus Tropheus, which belongs to the tribe Tropheini according to Poll (1986): T. annectens Boulenger 1900, T. duboisi Marlier 1959, T. brichardi Nelissen& Thys van den Audenaerdehys 1975, T. kasabae Nelissen 1977, and T. polli Axelrod 1977.
In contrast to all the other Tropheus species, which have between five and seven spines on their anal fin, both T. annectens (a uniformly dark brown species from the central West Coast) and T. polli (distributed on the central East Coast) have only four. A characteristic feature of T. brichardi, occurring in Burundi, is a saddle-like yellow blotch below the front section of its dorsal fin.
The description of T. kasabae by Nelissen, which was based on specimens he received from the aquarium trade, raises questions because it is not without errors. According to the author’s explanation, the specimens were caught in Kasaba Bay in Zambia and exported by Misha Fainzilber, with whom I was in close contact in those days. However, Fainzilber’s export station was based in Dar es Salaam in Tanzania, and he never caught or exported aquarium fish from Zambia. A photo of T. kasabae in Nelissen’s description and his reference to one of my publications (Staeck, 1975) give reliable evidence that his description does not concern the Tropheus population occurring in Kasaba Bay, but another one known as “rainbow moorii,” which is distributed further to the south near Cape Chaitika.
The type locality of T. moorii is Kinyamkolo. This village, situated in Zambia at the southern end of Lake Tanganyika, is known as Mpulungu today. All the confirmed collection sites of this species are situated on the eastern shore, between this locality (Kumbulu Island, Mutondwe Island) and the vicinity of Kala in the south of Tanzania (Sturmbauer & Meyer, 1992). The first color photo of a specimen from the vicinity of Mpulungu was published in the mid-1970s (Staeck, 1975). The first live specimens of T. moorii were imported to Germany in 1978.
The coloration of T. moorii from collecting sites near Mpulungu varies from dark olive green to a greenish brown. In the middle of the body (on the sides) there is a yellow or orange blotch of varying form and size. In Zambia, the dorsal fin is gray or bluish, and in some localities in Tanzania, it is purple or reddish. On the head are numerous tiny bright dots. Apart from a dark area in its upper part, the iris is silvery, and the eye has a narrow reddish rim. Young specimens show a pattern of approximately nine narrow vertical stripes, which usually disappear in adult fish. Among the many names used in the past for T. moorii by aquarists are sunset moorii, red rainbow moorii, and lemon blotch moorii.
The genus Tropheus is not just popular among aquarists. In the past few decades, many scientists also took a keen interest in these cichlids, as their study promised new insight into the progress of evolution and the process of speciation. Tropheus populations live exclusively in rocky habitats of the upper littoral zones of the lake. Although they can be found in deeper water, they are most abundant at depths approximately 1 to 3 meters (3 to 10 feet). In such shallow areas, these cichlids often occur in surprisingly high numbers—they are social fish that live in close contact to conspecifics.
Tropheus species are spread over the rocky shorelines of Lake Tanganyika in countless populations isolated from one another by geographic barriers. During their evolution, these populations gradually changed due to the development of various factors, which include coloration, morphology, anatomy, ecology, and sometimes even their behavior. However, even neighboring populations may vary considerably to the degree that they possess different features. Sometimes the differences between them are only slight, but in about a half dozen cases, the dissimilarity is so marked that these populations were described as separate subspecies or species. In several localities, two (or sometimes even three) different Tropheus species are syntopic (i.e., they live together in the same area).
The most important factors causing the diversification of the Tropheus populations are mutations, but, in addition to their peculiar feeding habits (and consequently, their pronounced habitat specificity), their fidelity to the upper littoral zones plays an important role in maintaining the reproductive isolation of the different populations. Some geographic barriers preventing the interbreeding of adjacent populations are sandy or muddy shores, river estuaries, and open water. All Tropheus strictly avoid sandy or muddy shores and open water because these areas are devoid of epilithic algae (aufwuchs) to feed on, as well as shelter from predators and suitable spawning sites. They also avoid river estuaries, as their water is murky, soft, and acidic, which contrasts from the clear, hard, and basic water of the lake proper.
The comparison of mitochondrial DNA sequences of different Tropheus populations (Sturmbauer & Meyer, 1992; Baric et al., 2003; Sturmbauer et al., 2005) produced the surprising results that adjacent populations are often not closely related, while populations distributed along the opposite western and eastern shorelines and isolated by 80 kilometers (50 miles) of open water sometimes unexpectedly possess an almost identical genetic makeup. These seemingly arbitrary patterns of their distribution can be explained as the result of a series of extreme changes in the lake level.
Three separate times during the course of its geological history, the level of Lake Tanganyika—which has a maximum depth of 1470 meters (4800 feet)—dropped by 600 meters (1950 feet) below its present level. These repeated extreme fluctuations would temporarily divide the lake into three isolated basins. On the one hand, populations that had been separated by barriers between their rocky shore habitats were able to comingle as their habitats were thrown together, while on the other, populations that had been neighboring were separated and took different evolutionary paths.
These changes strongly influenced the distribution of the Tropheus populations, for several of them were able to colonize additional sections of the coast where they came into contact with the original colonizers,sometimes even replacing them. Some populations even crossed the lake along ridges between the three temporary lake basins in its central region. In these smaller basins, these groups were found on both shores, but when the water rose again, creating a large open-water separation, they became isolated on opposite shores and had a different evolution.
All Tropheus are specialized aufwuchs eaters characterized by their pronounced food specificity and peculiar feeding behavior. In the lake, they are strict herbivores that bite and tear off bits of multicellular epilithic algae growing on the surface of rocks or stones. Their numerous outer bicuspid and tricuspid jaw teeth make it possible to browse a large quantity of algae per bite. While browsing, the fish usually turn their head distinctly from one side to the other. Ecological studies revealed that 88 percent of their stomach contents were made up of filamentous algae. Yamaoka (1983), who studied the feeding behavior of a population on the northwestern coast near Luhanga, as well as the so-called cherry spot moorii on the east coast close to the Mahale Mountains, observed that females regularly fed on algae even when brooding eggs or larvae in their mouths.
In the aquarium, all Tropheus are opportunistic feeders, greedily eating any foods offered to them. Earthworms and beef heart, however, are not proper foods for these specialized herbivores, since they need a varied diet rich in roughage. Tubifex worms and bloodworms (chironomid larvae) should not be used as food either; they are too high in protein for these vegetarians.
A characteristic of all Tropheus species is extremely high aggression towards conspecific individuals. In small tanks without adequate living space, the high frequency of attacks and fights between these cichlids will inevitably result in losses. There is strong evidence from ecological studies that a tight correlation exists between their deep-rooted intraspecific aggressiveness and their specific feeding behavior. As explained above, in their natural habitats these cichlids are strict herbivores that feed on algae growing on the surface of rocks and stones in the upper littoral zone. Since this food source is limited, both sexes of the fish have to defend their own feeding territory, guaranteeing their feeding places in order to prevent overexploitation of these resources.
Kawanabe (1981), who studied a population at Luhanga on the northwest shore of the lake, found that the size of the feeding territories was between 0.2 and 1.2 square meters (2 and 13 square feet), averaging 0.8 square meters (9 square feet) overall. In suitable habitats, where the number of individuals is very high, the territories cover the bottom of the lake like a patchwork quilt. At night, however, most of the fishes leave their own territories to seek shelter from predators under rocks where several individuals often crowd together. Although Kawanabe did not mark the fishes, he found reliable evidence that most of them returned to the site of their former territory every morning.
Kuwamura (1986) found that the mating territories of Tropheus species are even larger than their feeding territories: Those of the so-called “cherry spot moorii” are 3 meters (10 feet) in diameter, and those of T. polli are 4 meters (13 feet) in diameter. The size of the feeding and mating territories documented in field studies explains why only two or three particularly dominant individuals usually show their conspicuous coloration in an aquarium, while all the other fishes—which cannot occupy a territory of their own and consequently suffer from continuous stress—hardly show any colors, but look more or less dark brown or blackish.
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[In Part 2, the author will continue his look at the fascinating Tropheus species with an examination of the aquarium care and breeding of these colorful cichlids.—Eds.]
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