Visit Tanzania II – and the Petrochromis horii species group

A well hidden dive spot in Tanzania is the habitat of Petrochromis sp. “Red” at Lyamembe.  First discovered by Horst Walter Dieckhoff at Luagala Point in Mahale Mountains National Park in 1986-87 (Konings 1988: 42-46; 1998: 50), the fish was rediscovered by the divers of African Diving in April 2002 at the near shore Lyamembe Reef. The reef is located in the centre of Lyamembe Bay, some 30 kilometres (km) south of Luagala Point and has a varying depth ranging from 4-26 metres (m). Due to suboptimal biotope and the quite shallow nature of the reef, P. sp. “Red” is rare at this locality, and adult individuals are quite seldom observed, though juveniles are seen more frequently. For the ornamental fish trade, the fish is collected several hundred metres off shore where deep water reefs are present. P. sp. “Red” is one of the lake’s most challenging fishes to collect due its free-swimming behaviour, large territories/roaming area, and deep water habitat. Second out in the series “Visit Tanzania” is such an off-shore locality called “Lyamembe Offshore Reef” at 6°27'36" S, 29°54'53" E.

Fig. 1. Lyamembe Village.

During a survey in 2007, the area off Lyamembe was searched with an eco-sounder in order to locate the exact coordinates for off-shore reefs. Rumours existed that local fishermen, fishing for food, caught large quantities of P. sp. “Red” with gill nets in deep water. Directed by two such fishermen, we searched the area in early December hoping to find a deep water habitat shallow enough to be able to dive. The day before, we had witnessed the fishermen’s catch of around 50 pieces males of P. sp. “Red” (see picture below). Surprisingly, no females were caught in their net. From the search, only one suitable locality was found: “Lyamembe Offshore Reef” (the given coordinates). This reef is located about 500 m off Lyamembe Bay and has a shallow point of 35 m. Scattered large boulders and rock formations on a white sandy bottom characterize the underwater landscape.  Several adult specimens of P. “Red” were observed in the habitat, both males (see picture below) and females. Also at the reef, a unique colour variant of Cyprichromis microlepidotus feels at home, and the area harbours one of the southernmost populations of Neolamprologus niger. Bright yellow females and pitch-black males are found in the sand beneath larger rocks. Adjacent to Mahale Mountains National Park, the Lyamembe area is inhabited by several unusually large crocodiles. At Lyamembe Offshore Reef, however, crocodiles are rarely seen due to its offshore location. Water cobras have been spotted at the reef, but, while in the water, the snake is friendly and hardly ever strikes, even at the closest encounter.

The small village of Lyamembe in Lyamambe Bay offers great camping possibilities (very friendly villagers) and comfortable accommodations are available in nearby Mahale Mountains National Park with several options (see external links). At TANAPA guest house, it is possible to buy provisions. Before entering the park, it is mandatory to report to the park rangers at the Mabilibili outpost (just 1.5 km north of Lyamambe). Also, permission from the park’s headquarters is required to enter from the south. As there is no phone service in the park, advance arrangements are necessary. Park fees are payable only at Bilenge headquarters in the northern part of the park (some 60 km to the north).

Camping sites southwards are available in the protected bays of Nanga and Makola, just 5 km from Lyamembe. And at the nearby villages Makola and Sibwesa, it is possible to buy basic provisions.

Fig. 2. Petrochromis sp. "Red" and P. ephippium are equally abundant at deep-water habitat of 35-40 m (in the picture, an individual of the latter species is discernible behind the P. sp. "Red"). In shallow water. P. ephippium clearly outnumbers P. sp. "Red" and, in depths less than 15 m, P. sp. "Red" is normally absent. It is expected that in deeper water (>50m), the relationships are the opposite. Pictures captured in December 2007.

Morphologically defined by the appearance of its brush-like jaw teeth, Petrochromis feeds on the unicellular algae attached on epilithic filamentous algae (Yamaoka 1983: 77). There are presently eight described species of Petrochromis, the latest addition to the genus being P. horii. Though, there is disagreement about the status of Petrochromis ephippium, being treated as synonymous with P. trewavasae (Takahashi and Koblmüller 2014). Intentioned as a biological subspecies of P. trewavasae by Brichard (1989: 401), Maréchal and Poll (1991: 373) continuously treat P. ephippium as such. But P. ephippium is sympatric with P. trewavasae at several locations in southern Congo (Konings 1998: 50), and they are distinct in appearance and behaviour, and prefer different types of habitat, which make them very unlikely conspecific. However, there has not been any type specimen of P. ephippium deposited in any museum collections (which after 1999 is mandatory for a name to be validly published), neither is there any clear information on the type locality (which is to be expected in a description) (Brichard 1989: 401). Introduced by Herrmann (1985b: 489), the colourful Petrochromis sp. “Moshi yellow” is very likely conspecific with P. ephippium, as suggested by Karlsson (1998: 34-35, figs., 45). Previous speculation suggested P. sp. “Moshi yellow” to be a possible conspecific to P. sp. “Red” (Konings 1998: 50), based on the fact that variants of P. sp. “Moshi yellow” (syn. P. ephippium) at Sibwesa, Lyamembe, and further north along the coast of Mahale Mountains, exhibit an orange colouration (vs. yellowish or brownish elsewhere). This variant  is also known as P. ephippium “Moshi orange”; and a similar variant of P. ephippium with orange finnage was documented by Staeck (1983: 324-325, fig.). However, P. ephippium is surely and without doubt distinct from P. sp. “Red”, the former being initially reported on by Staeck (1977: 211, 274, fig. top) as similar to P. trewavasae, and observed in the lake at Kigoma and in the border area of Zambia and Tanzania; later on introduced with its specific name by Zadenius (1982: 8) as Petrochromis spec ephippium, seven years prior to its formal description, when it was reported [translated from Swedish]: “In the lake it becomes all yellowish and is instantly observed in its habitat.”

The latest of the congeners is Petrochromis horii. It was discovered by M. Hori at Kasenga, slightly northeast of Mpulungu, around 1996 or earlier (Takahashi and Koblmüller 2014). During its discovery it was considered being “similar to P. fasciolatus in body colouration and stripe pattern but did not have a protruding lower jaw... “ (Takahashi and Koblmüller 2014) This observation is similar to Herrmann’s (1985b: 490) statement on the similarities between P. fasciolatus and P. sp. “Gold” [translated from German]: “...at a first look it is very similar to P. fasciolatus, regarding body shape and colouration...[but] the mouth is terminal and the jaws equally protruding”.

Petrochromis horii was recognised as a distinct species based on both morphological and molecular analyses, and congeneric species from all major groups (so-called “Operational Taxonomic Units”), as well as all described species, of the genus were included in the analyses, except for Petrochromis sp. “Gold” and related species, which were only included in the molecular analysis, not in the morphological. P. horii proved to be morphologically distinct from all other species, but appeared closely related molecularly to P. sp. “Katete”. An mtDNA based phylogeny is suggesting the two species to be potentially conspecific (Takahashi and Koblmüller 2014). P. sp. “Katete” is very likely synonymous with P. sp. “Yellow” (Herrmann 1987: 142, 137, fig. top right; 1994: 14-17) and P. sp. ”Gold” (Konings and Dieckhoff 1992: 179, fig; Konings 1996: 94; 1998: 186). If also morphologically compared, P. sp. “Gold” (syn. “Katete”, “Yellow”) and P. horii would likely prove to be closely related in such a study as well.

From both personal experiences and public reports, we have learnt that Petrochromis sp. “Red” or closely related species occur in the whole southern part of the lake, i. e. continuously all around the shores, from Mahale Mountains at the central east coast via the Zambian coast to Cape Tembwe at the central west coast. Due to habitat-specific restrictions and deep water living conditions and thereby an obvious seclusion, plus an occasional inconspicuous colouration, the group is suggested to possibly have an even wider distribution in the lake. Based on unifying attributes, such as gross morphology, behaviour, physiology, ecological* preference, these species may together be regarded as a species group, in this case a monophyletic group of allopatrically isolated species. They are considered being distinct species, but closely related based on several attributes of traits (variable) and characters (non-variable). Pending a taxonomic study of all of the species, only gross differences/similarities are identified and mentioned. The species are the following:

1. Petrochromis sp. “Red”; occurs in the east central part of the lake; characterized by conspicuous sexual colourational dimorphism (adult males differ in colouration from females and juveniles; intensive red vs. brown).

2. Petrochromis sp. “Red mpimbwe”; occurs in the south eastern part of the lake; characterized by dark brown conspiciuously striped juveniles and dark brown partially striped adults with only weak dimorphism among sex; females tend to be more obviously striped than males. Populational differences in terms of being more or less red, orange or yellow. This species was introduced as P. sp. “Mpimbwe” from Cape Mpimbwe by us in 1991 (Zadenius 1991a: 37: “an unusual species, [in aquarium] brown yellowish with yellowish finnage”; Zadenius 1991b: 44-45: “A brand new deep living Petrochromis from Mpimbwe area, which has proven to be very peaceful. It is collected at a depth of 35 metres where it is occuring very sporadically”), but soon thereafter changed to P. sp. “Red mpimbwe” (Johansson 1994: 43; Johansson and Uusiportimo 1994: 43, fig.), by which it was exported for about ten years. The deep living habit of P. sp. “Red mpimbwe” was further documented by us in a species inventorial diving log from Cape Mpimbwe (Lundblad and Karlsson 1992). In 2002 when we found P. sp. “Red” at Lyamembe, and realized that the two species were practically identical, less colouration, we referred to both as P. sp. “Red”. We also considered P. sp. “Red” and P. sp. “Gold” to be potentially the same species, when we in 2003 displayed pictures of each species’ juveniles on our website mounted side by side, to demonstrate the similarities (see crop of 2003 website below). The southernmost variant was discovered at Kambwimba during a survey in 2008 when P. sp. “Red mpimbwe” was found at every rocky location from Karema all the way south to Kalambo River. Samples were collected at various locations, including Kambwimba, just north of the river. This variant, which was subsequently named “Flame tail”, was recently mentioned by Takahashi and Koblmüller (2014) as resembling P. horii; deposited at the Swedish Museum of Natural History. The variants in Kipili area and south to Fulwe Rocks, known as P. sp. “Kipili brown” (Konings 1996: 96; 1998: 50) are conspecific with P. sp. “Red mpimbwe”.

Fig. 3. Petrochromis sp. “Red” from Lyamembe and P. sp. “Gold” from Mtoto. The individuals were displayed side by side to demonstrate the similarities. Extract from African Diving Website; Display; Petrochromis page 5; August 2003.

3. Petrochromis horii; occurs in the most southern part of the lake, at Kasenga in Zambia, but likely further to both east and west. Morphology is limitedly known, but it seems to be characterized in colouration by a “moss green or dark green” body (appears very lightly coloured in photograph); and no apparent sexual differences, the largest specimen being a female (137.6 mm SL), suggesting the possibility of a reversed sexual dimorphism in body size (Takahashi and Koblmüller 2014), which seems less likely given corresponding characteristics of the other three species.

4. Petrochromis sp. “Gold”; occurs in the south western and west central part; characterized by an ontogenetical dimorphism (juveniles and adults completely differ in colouration; bright yellow vs. grey). P. sp. “Gold” has been documented as being rare in its natural habitat, which is basically due to its deep-living habit. From reports by Staeck (1994: 11): During three trips to the lake it was observed only twice; the first time in relatively shallow water when snorkel diving; both times at depths of 10-15 metres in Cameron Bay; and both individuals sub-adults. The idea, or statement, that only juveniles of P. sp. ”Gold” and not adults exhibit the bright yellow colouration, was presented in the same report (Staeck 1994: 13), and confirmed by Herrmann (1994: 15) based on aquarium studies made in 1983. An alternative view was presented by Brichard (1989: 396) thinking of P. sp. “Gold” as a small species, not growing larger than the observed yellow individuals, a view which was supported by Büscher (1994: 14). Büscher added to the fact that also very small juveniles (3 cm) are yellow (see also Herrmann 1985a: 443, fig. bottom), and further reported on a natural distribution between Cape Kashese and Mwerazi; and Konings (1996: 94) between Katete to Mtoto. Based on personal experience, we can also include Cape Tembwe to its natural surroundings, and confirm that adult individuals (15-20 cm) in the lake are not yellow; they are dark grey and commonly striped.

Fig. 4. Petrochromis sp. "Red Mpimbwe” in aquarium in Dar es Salaam, Tanzania: the very first individuals, collected at Cape Mpimbwe in 1991. The individuals were exported to Åleds Akvarium, Sweden September 6, 1991 (Zadenius 1991a).

The species group may be referred to as the Petrochromis horii species group. Some of the unifying characters are morphological (body pattern of vertical bars appearing the same, absence of egg-spots, almost identical shape and size of body); behavioural and physiological plus ecological* preferences (a curious species not easily scared away, relatively weakly territorial and mildly aggressive, usually living in deep water with sandy surrounding and occasional large rocks; semi-pelagic lifestyle, i. e. may keep a notable distance from substrate and  rocks vs. among rocks as seen in congenerics). Separating characters are basically morphological (e. g. colourational differences, ontogenetical dimorphism). Major rivers that flow into the lake, mark the distribution of the different species.

The four species are presumably diagnosable units: distinct phylogenetic species. They are nevertheless highly likely closely related, and would not unlikely end up as sisters on a cladogram. They are a species group, a taxon larger than species but smaller than genus, of allopatrically isolated species. Alternatively, they may together be treated as a polymorphic superspecies, as recently suggested for two of the species (Tawil 2010).

* Ecological specifications are not considered as diagnosable characters, but rather as an indication that such may be present. Regarding attributes, traits and characters: Kullander (1999), Wiley and Lieberman (2011).

External links:

TANAPA Mango Tree Bandas (mid-range, budget):

Greystoke Mahale (exclusive):

Kungwe Beach Lodge (exclusive):

Flycather Camp (mid-range):


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