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Lake Mala i is known for its endemic haplochromine species flock, most notably the rock-dwelling cichlids known as mbuna. One of the larger genera of mbuna is Metriaclima, a group consisting of 31 described species (including the five described herein) and approximately 45 recognized unique populations. Metriaclima is diagnosed by its feeding behavior and several morphological characteristics including the angle of the vomer and the presence of bicuspid teeth in the outer row of both the upper and lower jaws. Metriaclima zebra, the type species for the genus, was described based on a single specimen. While the collection location of this holotype is not known, based on the travel records of its collector, it is likely that the specimen originated from Likoma Island. The holotype was therefore compared to specimens from several localities around this island and was found to be morphologically indistinguishable from some of these. This study includes the morphological analysis of 496 specimens of Metriaclima belonging to 31 collections from Lake Mala i. Morphometric differences were analyzed and the relationships among several distinguishable populations of Metriaclima zebra were investigated. Our study further resulted in the description of the following five new species belonging to the M. zebra species complex: M. pambazuko, M. lundoense, M. midomo, M. tarakiki, and M. nigrodorsalis. These species were distinguished and described based on color patterns, morphometric, meristic, and ecological differences. These new species were compared with and distinguished from nearby populations of Metriaclima having similar pigmentation patterns and/or similar ecological niches. An artificial dichotomous key to the described species of Metriaclima is presented.

In the first half of this century, Lakes Victoria, Kyoga and Nabugabo had a diverse and similar native fish fauna (Graham, 1929; Worthington, 1929; Cambridge Nabugabo Biological Expedition, 1962). The fisheries of these lakes were based on about 14 fish taxa of which two were tilapiine cichlids; Oreochromis esculentus and O. variabilis were the most important. The haplochromine cichlids were represented by more than 300 species in Lake Victoria, more than 99% of them endemic (Greenwood, 1974; Witte et al., 1992a, b). These formed at least 80% of the demersal fish stocks in Lake Victoria up to the 1980s (Kudhongania and Cordone, 1974; Okaronon et al., 1985). Haplochromine cichlids were also abundant in Lakes Kyoga and Nabugabo (Worthington, 1929; Cambridge Nabugabo Biological Expedition, 1962).

Before the decline of the species flock of haplochromine cichlids of Lake Victoria due to the Nile perch upsurge, there were many co-existing haploehromine species such as the taxonomically and ecologically well-studied zooplanktivores of the Mwanza Gulf. In spite of the scarcely separated niches of some of these species, no sign of competition for space or food could be demonstrated. As is argued in this paper, optical differentiation could well be an aspect of adaptive radiation of these zooplanktivores, particularly among the highly sympatric species. Our hypothesis is based on the morphological modifications of retinal structures in nine zooplanktivorous species. Interspecific variation was observed in composition, size and density of the photoreceptors and ganglion cells. The analyses included the intraretinal variation and size dependency of some of the structural parameters. The optical functions deduced from retinal structure indicate distinct interspecific differences in sensitivity thresholds and a slight differentiation in visual resolution. These functions correlate poorly with the photic conditions of the species-specific habitats. The optical properties can, on the other hand, be connected with the more subtle differentiation in food items and feeding behaviour among these species. It is our concluding hypothesis, that the optical differentiation among the haplochromine zooplanktivores primarily served resource partitioning by different modes of visual prey detection rather than niche partitioning by habitat.

The photoreceptors of four co-existing haplochromine cichlids have been studied morphometrically and microspectrophotometrically, and the results were interpreted in terms of resolution and sensitivity. Among the three species, Haplochromis argens, H. piceatus and H. ishmaeli, the cone dimensions and the visual pigments differed only slightly, in spite of differences in vertical distribution and feeding behaviour between these species. The fourth species H. pyrrhocephalus showed distinctly different visual properties, with very large double cones at low densities, and its spectral sensitivity shifted to significantly longer wavelengths. To some degree, the photoreceptor morphometrics and visual pigments appeared to be attuned to the photic conditions of the specific habitats. The two species H. piceatus and H. pyrrhocephalus, occupying a dimmer habitat with less penetrating blue light, had reduced blue sensitive single cones, whereas the surface dwelling species H. argens had relatively small red/green sensitive double cones. Also an attempt has been made to relate the visual capacity of the cichlids to their behavioural patterns, focussing on prey detection. The greatest visual differences were observed in the two species H. argens and H. pyrrhocephalus, with resources coincidence and with the highest encounter frequency, which may indicate that visual segregation contributes towards reducing interference competition among co-existing species with a similar diet.

The introduction of Nile perch, Lates niloticus, to Lake Victoria in the late 1950s has incited much controversy and discussion, primarily because of the subsequent dramatic loss in species diversity and abundance of a unique haplochromine group (Barel et al., 1985, 1991; Coulter et al., 1986; Payne, 1987; Ribbink, 1987; Bruton, 1990; Witte et al., 1992a,b). Four species of tilapias were also introduced, the Nile tilapia, Oreochromis niloticus, successfully. For 20 years, while traditional fish catches continued to decline, catches of Nile perch were minimal. Then in the early 1980s the Nile perch population boomed and by 1990 the total annual catch from Lake Victoria had increased fivefold, to over 500 000 t (tonnes) (Fig. 7.1). The lake now supports a thriving fishery and supporting industries (Reynolds and Greboval, 1988; Greboval, 1990; Chapter 10). Catches of traditional species have further decreased and the fishery now largely comprises three species: the total demersal exotics, Nile perch and Nile tilapia and a native zooplanktivorous, pelagic cyprinid, Rastrineobola argentea, the dagaa or omena (Chapters 2–11).

Human activities have had profound impacts on almost all freshwater ecosystems in the world. These activities include mechanical changes such as damming or drainage as well as chemical effects like eutrophication and pollution, all with some effects on fish communities. Against this background of massive, worldwide and direct human impacts on freshwater ecosystems, the effects of fish introductions may seem to have only very modest effects on fish communities (Fernando, 1991). However, the increasing concern about the loss of global biodiversity and the recent mass extinction of haplochromine cichlids in Lake Victoria associated with the introduction of the piscivorous Nile perch (Witte et al., 1992; Chapters 2–11) has led to renewed research efforts on the effects of species introductions, especially in relation to commercial exploitation.

Lake Victoria, the largest tropical lake in the world (Fig. 6.1), was until recently a typical cichlid lake. Eighty percent of the demersal ichthyomass of this East African lake consisted of haplochromine cichlids (Kudhongania and Cordone, 1974a, b). The more than 300 haplochromine species, of which 99% were endemic, exploited virtually all food sources in the lake (Greenwood, 1974, 1981; van Oijen et al., 1981; Witte and van Oijen, 1990). Each species had its own unique combination of food and habitat preferences (e.g. van Oijen, 1982; Goldschmidt et al., 1990). The haplochromines were only locally important to fisheries (Kudhongania and Cordone, 1974a). In the 1970s a small-scale trawl fishery on these fishes was developed in the southern part of the lake near Mwanza. At that time the mean catch rate was more than 1000 kg h-1 (Goudswaard and Ligtvoet, 1988; Barel et al., 1991; Witte et al., 1992b).

Lake Malaŵi is home to at least 500 and possibly as many as 2000 fish species which are endemic or unique to the lake. These may account for as much as 2–5% of all existing vertebrate species. Almost all of them belong to one family, the cichlids, and apart from three tilapiines, all are closely related haplochromine species, possibly descended from a single, recent common ancestor (Meyer et al., 1990, 1991). Understanding the mechanisms of the evolution of this diversity may provide one of the most critical tests of models of the origin of species (Mayr, 1984; Turner, 1994a). In addition to their great scientific importance, the fishes of Lake Malaŵi are an important component of the aquarium fish trade, a major tourist attraction and perhaps of considerable potential in aquaculture.

Prelude to ecomorphology of fishes E.K. Balon, K.F. Liem. Introduction. Perspectives on the ecomorphology of bony fishes P.J. Motta, et al. Review. Development of ecomorphology of fishes in Russia S.A. Smirnov, et al. Full papers. Ecomorphological correlates in ten species of subtropical seagrass fishes: diet and microhabitat utilization P.J. Motta, et al. A functional approach to ecomorphological patterns of feeding in cottid fishes S.F. Norton. The influence of oral anatomy on prey selection during the ontogeny of two percoid fishes, Lagodon rhomboides and Centropomus undecimalis J.J. Luczkovich, et al. Predicting patterns of prey use from morphology of fishes P.C. Wainwright, B.A. Richard. Ecomorphology of retinal structures in zooplanktivorous haplochromine cichlids (Pisces) from Lake Victoria H.J. van der Meer, et al. Ecomorphological adaptations to bioluminescence in Porichthys notatus A.F. Mensinger. Ecomorphology of solitary chemosensory cell systems in fish: a review K.Kotrschal. Tradeoffs between respiration and feeding in Sacramento blackfish, Orthodon microlepidotus J.J. Cech Jr., M.J. Massingill. Time and tide wait for no fish: intertidal fishes out of water K.L.M. Martin. Papyrus swamps and the respiratory ecology of Barbus neumayeri L.J. Chapman, K.F. Liem. Morphology, mechanics, and locomotion the relation between the notochord and swimming motions in sturgeon J.H. Long Jr. Evolutionary interplay between ecology, morphology and reproductive behavior in threespine stickleback, Gasterosteus aculeatus S.A. Foster, J.A. Baker. Armor morphology and reproductive output in threespine stickleback, Gasterosteus aculeatus J.A. Baker, et al. Ecomorphological diversification and convergence in fluvial cichlid fishes K.O. Winemiller, et al. Phylogenetic systematics and biomechanics in ecomorphology M.W. Westneat. Summary. The role of ecomorphological studies in the comparative biology of fishes S.F. Norton, et al. Species and subject index.

Contributors. Series Foreword. Preface. General Introduction. Species change and fisheries in African Lakes: outline of the issues. Part One:- introduced Nile perch in Lake Victoria: Impacts on biodiversity and evaluation of the fishery: Impact of environmental change, species introductions and ecological interactions on the fish stocks of Lake Victoria. Limnological changes in Lake Victoria since the Nile perch introduction. Impact of fish species introductions on the tilapias of Lake Victoria and Kyoga. Diversity and stability of fish stocks in Lake Victoria, Kyoga and Nabugabo after establishment of introduced species. Dynamics of the haplochromine cichlid fauna and other ecological changes in the Mwanza Gulf of Lake Victoria. An analysis of species change in Lake Victoria: did the Nile perch act alone?. Analysis of species change in Lake Victoria using ECOPATH, a multispecies trophic model. Assessment of the Nile perch fishery in Lake Victoria. Thirty years on: the development of the Nile perch fishery in Lake Victoria. Socio-economic impacts of introduced species in Lake Victoria fisheries. Part Two:- evaluation of species change in other African lakes with introduced fish species: Inshore fish population and species changes in Lake Kariba, Zimbabwe. The impact of an introduction of sardine into Lake Kivu. The persistence of two introduced tilapia species in Lake Naivasha, Kenya, in the face of environmental variability and fishing pressure. Species change in reservoir fisheries following impoundment: the case of Lake Itezhi-tezhi, Zambia. Part Three:- evaluation of species changes in African lakes without introduced species: Changes in species composition and abundance of fish populations in Lake Turkana, Kenya. Management, conservation and species changes of exploited fish stocks in Lake Malawi. Changes in demersal cichlid communities as a result of trawling in southern Lake Malawi. Changes in species composition and abundance as a consequence of fishing in Lake Malombe, Malawi. Effects of exploitation on the pelagic fish community in the south of Lake Tanganyika. Changes in the pelagic fisheries of northern Lake Tanganyika during the 1980s. Part Four:- overviews of fish introductions in African Lakes: Genetic impacts of fish introductions: a perspective on African lakes. Fish introductions in the African Greak Lakes: some special characteristics. Thinking th unthinkable: a candidate model for predicting sustainable yields of introduced fish species in African lakes. Why is Limnothrissa miodon such a successful introduced species and is there anywhere else we should put it? Appendix: summary of characteristics of major African lakes. Author index. Species index. Subject index.

Color and pigmentation patterns of animals are often targets of sexual selection because of their role in communication. Although conspicuous male traits are typically implicated with intersexual selection, there are examples where sex-specific displays play a role in an intrasexual context, e.g. when they serve as signals for aggression level and/or status. Here, we focus on the function of a conspicuous male ornament in the most species-rich tribe of cichlid fishes, the haplochromines. A characteristic feature of these ca. 1500 species are so-called egg-spots in form of ovoid markings on the anal fins of males, which are made up of carotenoid based pigment cells. It has long been assumed that these yellow, orange or reddish egg-spots play an important role in the courtship and spawning behavior of these maternal mouth-brooding fishes by mimicking the eggs of a conspecific female. The exact function of egg-spots remains unknown, however, and there are several hypotheses about their mode of action. To uncover the function of this cichlid-specific male ornament, we used female mate choice experiments and a male aggression test in the haplochromine species Astatotilapia burtoni. We manipulated the number and arrangement of egg-spots on the anal fins of males, or removed them entirely, and tested (1) female preference with visual contact only using egg-traps, (2) female preference with free contact using paternity testing with microsatellites and (3) male aggression. We found that females did not prefer males with many egg-spots over males with fewer egg-spots and that females tended to prefer males without egg-spots over males with egg-spots. Importantly, males without egg-spots sired clutches with the same fertilization rate as males with egg-spots. In male aggression trials, however, males with fewer egg-spots received significantly more attacks, suggesting that egg-spots are an important signal in intrasexual communication.

The early development of the southern mouthbrooder, Pseudocrenilabrus philander, is documented from activation until the early stages of the juvenile period. The duration of the embryonic period is about 14 days at 25° C. Development is direct and there is accelerated exogenous feeding into the embryonic period. The pattern of development and the timing of ontogenetic events and structure formation are a reflection of both internal and external environmental conditions. During mouthbrooding, oxygen uptake is facilitated by embryonic respiratory plexuses and flapping of the pectoral fins. At the time of first release from the buccal cavity, the embryos are in an advanced state of development. The switch-over from the temporary embryonic respiratory system to the adult branchial system has occurred. The yolksac serves as a supplemental source of nutrition as the embryos develop their external food-gathering abilities. The skeletal and sensory systems are sufficiently developed to allow the young to return to the safety of the female’s buccal cavity. Pigmentation may provide disruptive colouration. The rate and pattern of development of another mouthbrooding cichlid, Oreochromis mossambicus, is similar to that of P. philander despite their phylogenetic differences, and may be a consequence of similar life-history styles.

In recent years the ichthyofauna of Lake Victoria, the world’s largest tropical lake, has gone through dramatic changes. The population of Nile perch, a large predator which has been introduced into the lake by man, increased explosively at the expense of many haplochromine cichlid species. At the same time, numbers of a small cyprinid (dagaa) rose sharply.

Although, generally, the origin of sex-limited traits remains elusive, the sensory exploitation hypothesis provides an explanation for the evolution of male sexual signals. Anal fin egg-spots are such a male sexual signal and a key characteristic of the most species-rich group of cichlid fishes, the haplochromines. Males of about 1500 mouth-brooding species utilize these conspicuous egg-dummies during courtship – apparently to attract females and to maximize fertilization success. Here we test the hypothesis that the evolution of haplochromine egg-spots was triggered by a pre-existing bias for eggs or egg-like coloration. To this end, we performed mate-choice experiments in the basal haplochromine Pseudocrenilabrus multicolor, which manifests the plesiomorphic character-state of an egg-spot-less anal fin. Experiments using computer-animated photographs of males indeed revealed that females prefer images of males with virtual (‘in-silico’) egg-spots over images showing unaltered males. In addition, we tested for color preferences (outside a mating context) in a phylogenetically representative set of East African cichlids. We uncovered a strong preference for yellow, orange or reddish spots in all haplochromines tested and, importantly, also in most other species representing more basal lines. This pre-existing female sensory bias points towards high-quality (carotenoids-enriched) food suggesting that it is adaptive.

Of the three cichlid species flocks in eastern Africa, Lake Tanganyika harbors the oldest species assemblage, which is also the most diverse morphologically and behaviorally. For 12 species (20 individuals) of 12 genera of the tribe Ectodini, 852 bp from two segments (cytochrome b and control region) of the mitochondrial genome were sequenced. In addition, orthologous sequences were obtained from eight species ( 11 individuals) representing other mouthbrooding lineages from Lake Tanganyika. Comparisons of sequence divergences revealed that the single Tanganyikan tribe Ectodini appears to be approximately five times older than the whole Lake Malawi cichlid species flock, suggesting that the radiation of the Tanganyikan mouthbrooding lineages took place long before the species flocks of Lakes Malawi and Victoria evolved. Seven of nine surveyed tribes of Tanganyikan cichlids appear to be approximately equally divergent, and this seems to corroborate the hypothesis of a rapid simultaneous formation of lineages at an early stage in the history of the Lake Tanganyika species flock. The close genetic relationship between the endemic Trupheus lineage and a nonendemic Haplochromine, Astatotilapia burtoni, indicates that members of the tribe Tropheini may be the sister group of the cichlid flocks of Lakes Malawi and Victoria. The phylogenetic analyses demonstrate the monophyly of the Ectodini and identify the Cyprichromini as their sister group among the Tanganyikan cichlids. Within the tribe Ectodini the molecular data suggest both a branching pattern different than that previously proposed and a subdivision of the Ectodini into four clades, instead of the two originally described. The previously postulated model of morphological transformations believed to be responsible for the drastically different types of ecological specialization found among the Ectodini might therefore be in need of reinterpretation. Characters immediately related to foraging and nutrition seem to be particularly prone to homoplasy, even among members of a single lineage of cichlid fishes.

The African Great Lakes are considered to be dynamically fragile ecosystems that are relatively resistant to minor changes with which they have co-evolved but vulnerable to major perturbations such as overfishing, the introduction of alien species and pollution. These lakes are inhabited by large species flocks of cichlid fishes which are characterised by a complex structure of interaction both between and within species, as is typical of mature ecosystems. Major perturbations, such as the disruption of trophic interactions through the introduction of alien fishes, may reverse the domination of relatively precocial, specialised forms and result in the creation of conditions that are conducive to the survival of more altricial, generalised forms with strong colonising abilities. The introduction of Nile perch and Nile tilapia, as well as other alien fishes, into Lake Victoria, combined with overfishing for the indigenous cichlid species, has resulted in marked changes to the fish communities and the fisheries that depend on them. The most important impacts of the Nile perch appear to be predation and aggressive effects whereas those of the tilapias include hybridization, overcrowding, competition for food and possibly the introduction of parasites and diseases. While the three proposed methods of conserving the indigenous flocks of cichlid fishes (captive propagation, reducing Nile perch stocks and closure of the haplochromine trawl fishery) all have merit, the changes that are occurring in Lake Victoria are basically irreversible. The highest priority should be to assist the governments of the riparian countries (Tanzania, Uganda and Kenya) with monitoring and research programmes and to support their policies of non-introduction of further alien fishes into any of the African Great Lakes so as prevent the same cycle of events from occurring, for example, in Lakes Tanganyika and Malawi. The diverse animal and plant communities of the African Great Lakes are a heritage of all mankind and it is the duty of every country to play a role in their conservation. It is therefore proposed that an internationally funded research programme should be mounted on the African Great Lakes on the scale of the tropical forest biome project of the IUCN.

About 50% of African cichlid species have been described. Little is known about cichlid ecology, behaviour or about the evolution and interactions of communities. Nevertheless, trends which provide an insight into cichlid life histories, into evolutionary alternatives and into behavioural alternatives which may be followed during the life time of these fishes are emerging. Cichlids which spend their entire life history in a single habitat belong to species flocks that have spectated greatly. In contrast, those groups which live in a variety of habitats during their life history have spectated little. Despite the trophic specializations that have occurred among cichlids, many and perhaps all species, have the ability to feed upon alternative food resources. They do so by switching or by markedly modifying their behaviour and all are particularly opportunistic. The extensive adaptive radiation of cichlids with regard to those attributes of morphology and behaviour that are associated with survival and growth, is apparently not matched by similar radiations in reproductive behaviour. The perceived evolutionary conservatism with regard to reproductive behaviour is attributed to the effects of stabilizing selection, but this still needs to be tested. The constraints of stabilizing selection appear to be lifted with regard to coloration. If colour is an important component of the specific-mate recognition system then it should also be subjected to stabilizing selection so the readiness with which colour variation occurs within and between populations needs explanation. Parental care in cichlids has followed a variety of evolutionary alternatives, all of which are geared to improve the chances of survival of offspring in their specific micro-habitats.

The cichlid species flocks of the African Great Lakes represent the most extreme case of adaptive radiation among vertebrates. Recently, attention has focused on the potential for sexual selection to drive or accelerate speciation in these fishes. Cichlids as a whole are social in nature and display complex behavior, particularly during courtship and spawning; however, the extent to which changes in species recognition cues may account for species diversity among haplochromine lineages has remained speculative. Our investigations have indicated that oral incubating haplochromines show a reduction in diversity and extent of courtship relative to substrate brooding cichlids, and apparently retain aspects of a primitive specific mate recognition system. Laboratory observations of courtship in the Malawian endemic Pseudotropheus zebra suggest that organization of the spawning bout is loose, and lacking in any well defined stimulus-response chain. Interspecific comparisons of in situ courtship behavior among male mbuna, lithophilous haplochromines of Lake Malawi, revealed only one potential example of species-specific behavior, and indicated that mate choice occurred prior to the onset of intense courtship. Courtship display by male mbuna does not appear critical to species recognition and may represent an evolutionary relict. Alternatively, male courtship display may have an indirect effect on successful reproduction or may be maintained through pleiotropic effects. The mbuna display no evidence of behavioral innovation and show limited interspecific differentiation in behavioral expression. More generally, there is no evidence at present to suggest that epigamic sexual selection, acting on courtship behavior, has been a major mechanism in the diversification of the haplochromine species flocks.

Background The exceptionally diverse species flocks of cichlid fishes in East Africa are prime examples of parallel adaptive radiations. About 80% of East Africa's more than 1 800 endemic cichlid species, and all species of the flocks of Lakes Victoria and Malawi, belong to a particularly rapidly evolving lineage, the haplochromines. One characteristic feature of the haplochromines is their possession of egg-dummies on the males' anal fins. These egg-spots mimic real eggs and play an important role in the mating system of these maternal mouthbrooding fish. Results Here, we show that the egg-spots of haplochromines are made up of yellow pigment cells, xanthophores, and that a gene coding for a type III receptor tyrosine kinase, colony-stimulating factor 1 receptor a (csf1ra), is expressed in egg-spot tissue. Molecular evolutionary analyses reveal that the extracellular ligand-binding and receptor-interacting domain of csf1ra underwent adaptive sequence evolution in the ancestral lineage of the haplochromines, coinciding with the emergence of egg-dummies. We also find that csf1ra is expressed in the egg-dummies of a distantly related cichlid species, the ectodine cichlid Ophthalmotilapia ventralis, in which markings with similar functions evolved on the pelvic fin in convergence to those of the haplochromines. Conclusion We conclude that modifications of existing signal transduction mechanisms might have evolved in the haplochromine lineage in association with the origination of anal fin egg-dummies. That positive selection has acted during the evolution of a color gene that seems to be involved in the morphogenesis of a sexually selected trait, the egg-dummies, highlights the importance of further investigations of the comparative genomic basis of the phenotypic diversification of cichlid fishes.

The explosive speciation of cichlid fishes in the African great lakes has intrigued biologists for many decades. Interest was revitalized in 1996 after the publication in Science of geological data [1] indicating that the youngest lake, Lake Victoria, must have been completely dry during the most recent Ice perhaps as recently as 12,400 years ago. This implies that the approximately 500 haplochromine cichlid species must have evolved within this extremely short timespan from a single ancestral species [2]. But even with lower estimates of species number and higher estimates of the age of the species flock, the haplochromine cichlids still present one of the most dramatic examples of speciation and diversification in vertebrates.

The adaptive radiations of cichlid fishes in East Africa are well known for their spectacular diversity and their astonishingly fast rates of speciation. About 80% of all 2,500 cichlid species in East Africa, and virtually all cichlid species from Lakes Victoria (~500 species) and Malawi (~1,000 species) are haplochromines. Here, we present the most extensive phylogenetic and phylogeographic analysis so far that includes about 100 species and is based on about 2,000 bp of the mitochondrial DNA. Our analyses revealed that all haplochromine lineages are ultimately derived from Lake Tanganyika endemics. We find that the three most ancestral lineages of the haplochromines sensu lato are relatively species poor, albeit widely distributed in Africa, whereas a fourth newly defined lineage – the 'modern haplochromines' – contains an unparalleled diversity that makes up more than 7% of the worlds' ~25,000 teleost species. The modern haplochromines' ancestor, most likely a riverine generalist, repeatedly gave rise to similar ecomorphs now found in several of the species flocks. Also, the Tanganyikan Tropheini are derived from that riverine ancestor suggesting that they successfully re-colonized Lake Tanganyika and speciated in parallel to an already established cichlid adaptive radiation. In contrast to most other known examples of adaptive radiations, these generalist ancestors were derived from highly diverse and specialized endemics from Lake Tanganyika. A reconstruction of life-history traits revealed that in an ancestral lineage leading to the modern haplochromines the characteristic egg-spots on anal fins of male individuals evolved. We conclude that Lake Tanganyika is the geographic and genetic cradle of all haplochromine lineages. In the ancestors of the replicate adaptive radiations of the 'modern haplochromines', behavioral (maternal mouthbrooding), morphological (egg-spots) and sexually selected (color polymorphism) key-innovations arose. These might be – together with the ecological opportunity that the habitat diversity of the large lakes provides – responsible for their evolutionary success and their propensity for explosive speciation.

Based on an extensive mitochondrial haplotype analysis representing about 900 specimens, we developed a conclusive model for the origin and age of the Lake Victoria (LV) superflock of haplochromine cichlids ([ 1 ][1]). Our most important findings were that (i) the cichlids were initially derived

Within the past two million years, more than 450 species of haplochromine cichlids have diverged from a single common ancestor in Lake Malawi. Several factors have been implicated in the diversification of this mono- phyletic clade, including changes in lake level and low levels of gene flow across limited geographic scales. The objectives of this study were to determine the effect of recent lake-level fluctuations on patterns of allelic diversity in the genus Metriaclima, to describe the patterns of population structure within this genus, and to identify barriers to migration. This was accomplished through an analysis of allele frequencies at four microsatellite loci. Twelve populations spanning four species within Metriaclima were surveyed. The effect of lake-level fluctuations can be seen in the reduced genetic diversity of the most recently colonized sites; however, genetic diversity is not depressed at the species level. Low levels of population structure exist among populations, yet some gene flow persists across long stretches of inhospitable habitat. No general barrier to migration was identified. The results of this study are interpreted with respect to several speciation models. Divergence via population bottlenecks is unlikely due to the large allelic diversity observed within each species. Genetic drift and microallopatric divergence are also rejected because some gene flow does occur between adjacent populations. However, the reduced levels of gene flow between populations does suggest that minor changes in the selective environment could cause the divergence of populations.

changes in fish faunal structure and diversity. Though catches of many species had declined by the 1960s due to overexploitation (Kudhongania et al., 1992), the dramatic increase in Nile perch in the 1980s in Lake Victoria was followed by a drastic decline in the populations of several indigenous species (Kaufman, 1992). Most notable has been the disappearance of over 50% of the endemic haplochromine cichlids from Lake Victoria (Kaufman, 1992; Kaufman et al., 1997). However, many indigenous noncichlids, some of which were important in the pre-Nile perch fishery, have also declined or disappeared (Kaufman, 1992; Kudhongania et al., 1992). Similar trends have been observed in other

were distinguished, two of which were major clades, represented by a large number of species. The other four lineages were each represented by a single species with a divergent mtDNA haplotype. One of the two major clades was composed of the shallow-water, rock-dwelling mbuna species, whereas the other included a diverse array of sand-dwelling and pelagic species. A number of taxa, found to be firmly embedded within the mbuna clade, are quite distinct in mor­ phology and generally inhabit deeper, sediment-rich areas rather than the rocky habitats typical of other mbuna. The mbuna group is generally thought to be a monophyletic assemblage, but these results suggest that it is actually paraphy­ letic. In contrast to the high morphological diversity among Malawi haplochro­ mine species, mtDNA sequence divergence was found to be remarkably low. This finding underscores the unprecedented rapidity of speciation and evolutionary plasticity in this fish species flock. B eginning with the earliest collections and vented identification of sister-group relation­ descriptions of Malawi haplochromines, ships (though many autapomorphic traits are taxonomists have been challenged and frus­ present). Second, an abundance of parallelism trated by attempts to reconstruct the phyloge­ has made it difficult to assure that shared traits netic history of this fauna. Two primary obsta­ are actually synapomorphic (Eccles and Tre­ cles have confounded this reconstruction. First, wavas, 1989). Early work on the Malawi ich­ a paucity of shared derived traits often pre- thyofauna revealed a large number of new spe­

Part 1 Phylogenetic intrarelationships of the family Chichlidae - an overview, M.L.J.Stiassny: Cichlid placement within the Percomorpha a review of Cichlid intrafamilial relationships concluding remarks Taxonomic appendix. Part 2 Distribition and ecology of the Cichlids of the African Great Lakes, A.J.Ribbink: geographic distribution ecology synthesis. Part 3 Ecology of Cichlids in South American waters and African rivers, R.H.Lowe-McConnell: neotropical Cichlid faunas the Cichlid faunas of African rivers riverine Cichlids associated with African lakes ecology of tilapias rheophilic Cichlids in Africa selection pressures on riverine Cichlids. Part 4 Speciation, P.H.Greenwood: speciation - the products speciation - the process. Part 5 Genetics, I.Kornfield: descriptive genetics genetics of the phenotype molecular systematics. Part 6 functional morphology, K.F.Liem: functional design of the feeding apparatus polyphyletic functional diversification or adaptive radiation?. Part 7 Feeding relationships, K.Yamaoka: feeding behaviour versatility in food and feeding behaviour how to coexist?. Part 8 Mating systems among Cichlid fishes, G.W.Barlow: an account of mating systems conservatism of mating systems factors of mating systems commentary. Part 9 Parental care, M.H.A.Keenleyside: general patterns of parental care behaviourial patterns associated with parental care male-female roles in parental care pair-bond stability during brood care brood-mixing evolution of parental care. Part 10 Ontogenty of behaviour in Cichlids, D.L.G.Noakes: developmental stages and the timing of hatching feeding behaviour social behaviour and the role of impriting parent-young interactions comparative studies. Part 11 Communication, M.Nelissen: what is communication? how do Cichlids communicate? functions of communication. Part 12 Sexual selection and the evolution of the Cichlid fishes of Lake Malawi, Africa, K.R.McKaye: overview of sexual selection theory field studies of Cichlid mate choice Lande's model of sexual selection upon polygamous species coloration and bower form-male characters undergoing sexual selection morphological and genetic evidence on monophyly of bower form evidence of female choice among lekking Cichlids in Lake Malawi. Part 13 The haplochromine Cichlids in Lake Victoria-an assessment of biological and fisheries interests, C.D.N.Barel: the original haplochromine species flock the impact of the Nile perch on the original haplochromine flock fisheries in Lake Victoria and their socioeconomic evaluation. Part 14 Cichlids in aquaculture, R.S.V.Pullin: why culture Cichlids? breeding cultured Cichlids world production of Cichlids in aquaculture aquacultural production appendix.

Until a few years ago, Lake Victoria possessed a large species flock of haplochromine cichlids, comprised of 250+ species. Very little was known about the possible ecological differentiation within trophic groups, and virtually nothing about the mechanisms structuring the community. This paper deals with zooplanktivorous species from the Mwanza Gulf of Lake Victoria that showed a large overlap in gross morphological characteristics. We found strong evidence that the species were ecologically segregated to a great extent. Species were restricted to certain horizontal and/or vertical zones. Species which segregated relatively little horizontally, did so vertically, and/or by different diet. The two species with the largest diet overlap segregated vertically. Species pairs segregated along at least one of the traditional niche axes: space, food and time. A detailed study of vertical distributions did not yield any evidence for interactive competition for space. Vertical distributions of fish and food at a 14 m deep station correlated well by night. By day the concordance was less clear.

Retinal parameters of the photopic system are determined in seven adult haplochromine cichlids. Resolving power is calculated as a function of the density of the twin-cones and the size of the eye-lens. The size of the twin-cones is considered to be a useful criterion to compare their sensitivity. Intra-retinal variation of the resolving power shows a negative correlation with the variation of the sensitivity of the photopic system. Interspecific variation of the resolving power and the sensitivity both show a positive correlation with the absolute eye-size. A maximum packing of the cones is approached in the examined species, except in Haplochromis microdon. Variation of the resolving power is discussed in relation with the theoretical value of the optical resolving power as calculated by OTTEN (1981). The significance of this variation is correlated with ecological data.

The insectivorous-molluscivorous haplochromine species belonging to the genera Gaurochromis Greenwood, 1980 and Labrochromis Regan, 1920 have been analysed. The degree of hypertrophy of the lower pharyngeal jaw, the apomorphic character for Labrochromis, is quantified and its intra-, interspecific and generic variability has been determined. Some measures for oral jaw-shape are given and the value of these for generic distinction is considered. In most, including apomorphic, characters L.ptistes overlaps with Gaurochromis and with other Labrochromis species. The overlap with the former genus is greater than that with the rest of the species of the genus in which it was placed by GREENWOOD (1980). L. humilior as described by GREENWOOD (1960), is a poly-specific taxon. The major part of the material is a-typical and belongs to a species which resembles an undescribed species from the HEST-collections. Together this material may bridge the gap between Gaurochromis and Enterochromis. The types of L. humilior deviate from Gaurochromis and Labrochromis in several aspects. The subgenera G. Gaurochromis and G. Mylacochromis are invalidated by G. iris and G. hiatus which fully bridge the subgeneric "gap". It is demonstrated that Gaurochromis plus Labrochromis species can be placed in continuous morphoclines on the basis of different characters, which include the apomorphic ones supposedly defining the seperate lineages. The only characters that show some discontinuity are oral jaw-lengths combined with head-length. However, oral and pharyngeal jaw-development are correlated and are shown to co-vary intraspecifically, so that the value for generic distinction is doubted. The problem of classification of haplochromines is discussed and the use of statistical methods such as principal component analysis is suggested. A conventional cladistic approach is not easily applicable in groups such as these lacustrine haplochromines.

In addition to the many trophic groups of haplochromine cichlids already known from Lake Victoria, two new ones (i.e. zooplanktophages and cleaner fishes) have been discovered by the Haplochromis Ecology Survey Team which operates in the Mwanza Gulf of the Lake. The present paper deals with the taxonomic description and eco-morphology of the two (new) species of haplochromine cleaner fishes. Cleaning symbiosis has been described mainly for marine fishes. Among cichlids only juvenile Etroplus maculatus were known as (facultative) cleaners 1 . The cleaning behaviour of the Victoria haplochromines is deduced from their stomach contents which revealed that one species feeds mainly and the other partly on carplice and leeches. No other cleaner fishes are known to feed on these kinds of parasites which in Lake Victoria occur externally on smooth-skinned fishes (Protopterus aethiopicus, Bagrus docmac, Synodontis sp. and Clarias sp.). The preference for firmly attached, flat parasites correlates with the scraper-like teeth of the haplochromine cleaners. Virtually all other cleaner fishes have teeth with pronounced, pointed cusps and feed on mobile parasites or (elongate) parasites which are only proximally attached to their hosts.

Lates niloticus is not native to Lake Victoria but was introduced during or shortly before 1960. It remained relatively uncommon until 1975, when the number in the Nyanza Gulf began to increase impressively, the estimated catch rising over 100-fold between 1978 and 1982. Originally Lates was piscivorous, its diet reflecting the composition of the native fish community. The present investigation has revealed that its diet is now almost entirely comprised of Caridina nilotica, a small microphagous prawn, and juvenile Lates. Native fish species, except for the small pelagic Rastrineobola argenteus, are very rarely consumed. This change in diet is a result of the shattering impact Lates predation has had on the native fishes, which have been virtually wiped out. The original community, which was dominated by several hundred haplochromine species and the catfishes Clarias mossambicus and Bagrus docmac which preyed upon them, and included two endemic tilapiine cichlids and 38 species of non-cichlids, no longer exists. It has been replaced by a community dominated by Lates which now accounts for well over 80% of the fish biomass in the Nyanza Gulf and very nearly 100% in the study area. The only other species regularly encountered were Oreochromis niloticus, an introduced tilapiine, and Rastrineobola argenteus, a native zooplanktivore.

This paper suggests that, on the basis of ontogenetic change in intestinal coiling pattern, four types and four subtypes could be recognized within 20 species of epilithic algal-feeding cichlids in Lake Tanganyika. The phylogenetically useful anatomical features characterizing each type are as follows. Petrochromis type: torsion of the intestinal tract generally occurs at Stage 5 Intersecting Point (IP), and the haplochromine loop and a two-loop coiling system are observable. Cyathopharynx type: the value of IP becomes 7 before torsion occurs, and the coiling system changes qualitatively from one-loop to two-loop types. Asprotilapia type: torsion occurs at Stage 5 IP, and a one-loop coiling system is retained throughout ontogeny. Telmatochromis type: no torsion occurs, and a one-loop coiling system is retained throughout ontogeny. Within the Petrochromis type, each of the four subtypes is characterized by the following features. Petrochromis subtype: the rostrally directed haplochromine loop has its rostral part situated to the right side of the stomach in the adult stage. Pseudosimochromis subtype: a circular haplochromine loop is present. Eretmodus subtype: the haplochromine loop tends to be prolonged and bends through 90 or 180 further counter-clockwise. Tropheus subtype: torsion occurs at Stage 7 IP.

Hybridization tests were carried out with the allopatric and sympatric haplochromine cichlids Haplochromis burtoni (Lake Tanganyika), H. nubilus (L. Victoria), H. elegans (L. George) and H. "black lividus" (L. Victoria). Female H. nubilus crossed with male H. burtoni produce lethal hybrids which do not survive the larval stage. The reciprocal cross, female H. burtoni x H. nubilus, produces F1, F2, F3 hybrids with a normal sex ratio, and fertile backcrosses F1 x H. burtoni and F1 x H. nubilus with a skewed sex ratio. In behavioral tests female H. nubilus spawn readily with H. burtoni males (lethal cross), whereas female H. burtoni spawn rarely with male H. nubilus (fertile cross). The inheritance of coloration, the "egg-dummies" pattern on the anal fin, and reproductive vigor in the hybrids are analysed in detail. Crosses which involve male H. elegans x female H. nubilus and male H. "black lividus" x female H. nubilus are fertile but have skewed sex ratios in favor of the females. The importance of environmental instability, learning and hybridization in cichlid fish speciation are discussed.

Aquarium-observations on a new paedophagous haplochromine species (Pisces, Cichlidae) showed that engulfing the snout of a brooding female to extract the brood, is a possible technique of gathering food, as was suggested by GREENWOOD (1959, 1974). Considering morphological information from various authors (GREENWOOD, 1959, 1974; BAREL et al., 1976, 1977) and notwithstanding some doubt expressed by FRYER & ILES (1972) and FRYER (1977), this snout-engulfing may be a widespread technique among the "larger mouthed" paedophages (i. e. in Lake Victoria: 6 out of 8 spp. described plus at least 8 new spp.). Snout-engulfing is the climax of a performance which resembles a fight, during which the paedophage also can force a brooding female to disgorge its brood by chasing and repeated attacks. The origin of snout-engulfing may be thought to lie in a modification of the fighting behaviour of a piscivorous ancestor, hunting on already jettisoned young still guarded by the female.

Cichlid fishes of the great East African lakes have been the subject of many evolutionary studies over the last decades. Over 100 haplochromine species have been described from Lake Victoria alone, many of which are endemic to that lake. Two recent studies, using enzyme electrophoresis, could not detect any genetic differentiation among the examined species. Consequently, it was concluded that the gene loci which were scored in these studies were not relevant to the genetic changes which occurred during speciation. Analyses of general protein electrophoretic patterns, however, does reveal differentiation on the supraspecific level. Three basic species groups can be discerned, each associated with ecological characteristics of these species such as diet and substratum. Implications for haplochromine evolution and taxonomy are discussed. Our data seem to support the hypothesis that trophic differentiation may have occurred within habitats, implying the possible importance of sympatric speciation in haplochromine evolution in Lake Victoria.

The endemic haplochromine cichlids from Lake Victoria are estimated to comprise 200 to 250 species. This estimate is mainly based on collections from two opposite ends of the Lake, i.e. the area around Jinja (Uganda) in the north and the area around Mwanza (Tanzania) in the south. An ecological and taxonomic survey of the haplochromines from the Mwanza area was recently started by the Haplochromis Ecology Survey Team (HEST). The collection of HEST contains several species groups of which the members closely resemble each other as well as their congeners known from the northern part of the Lake. One such case, the "H." empodisma group, has been analysed in this paper. The study was focussed on two new colour forms of this group, which were discovered in the Mwanza area, and on two previously described species, "H." empodisma and "H." obtusidens, which closely resemble them. It is demonstrated that the two species plus the two colour forms can be distinguished from each other on the basis of (small) morphological differences (other than male colouration). The two Mwanza forms are described as new species. The species rank is corroborated by ecological data.

Comparisons can be made between data collected by HEST in the Mwanza Gulf of Lake Victoria and that accumulated from Lake Malawi by the Fisheries Research Unit of the Malawi Fisheries Department. Although the sampling programmes differ the data available are sufficient to show many similarities between the ecology of the two species flocks. In each lake distribution and abundance of species are shown to be strongly influenced by both depth and bottom type, though the degree of association with the substrate varies between species. Well marked and comparable trophic groups are present in both lakes though in Lake Malawi it has been found that even species with highly specialised trophic mechanisms can be facultative feeders. This has not been demonstrated in Lake Victoria. A gradation from discrete breeding seasonality to continuous breeding appears to be a feature of the haplochromines of both lakes. Seasonality may be related to food supply or other factors such as weather conditions. The most notable difference between the two species flocks is that many species from Lake Malawi have restricted distributions within the lake whereas there is, as yet, no evidence for this in Lake Victoria.

Preliminary results of stomach content analysis of piscivorous haplochromine cichlids from the Mwanza Gulf of Lake Victoria indicate that the members of this trophic group are specialized predators. Although able to feed on a range of organisms, the various species have a strong preference for certain food items. Besides specialization on prey species, prey size partitioning plays an important role (especially among the predators of haplochromines). The food specializations are often correlated with habitat restrictions. The diversity of food and habitat preferences are reflected in the morphology of the piscivorous group which also indicate the existence of various predation techniques. The resulting resource partitioning contradicts the prevailing notion that many haplochromine cichlids in Lake Victoria feed on the same food items in a similar way.

The present study deals with the development of the skeletal elements of the pharyngeal jaw apparatus and their articulation with the neurocranium in a generalized haplochromine species, Astatotilapia elegans ( = Haplochromis elegans). Problems of the homology of the elements constituting the upper pharyngeal jaws are discussed. In early developmental stages the paired articular facets of the neurocranial apophysis are formed by the parasphenoid bone. During further development the basioccipital bone grows anteriorly and the surface area of each articular facet increases. We hypothesize that the bone-like material on the upper pharyngeal jaws and skull base apophysis is deposited by calcification of a type of adventitious cartilage.

The haplochromine Cichlidae endemic to Lake Victoria are recently estimated to comprise approximately 200 species. Morphologically these species vary within narrow limits but ecologically they demonstrate a wide and continuous spectrum of adaptations. Except for the papyrus swamps, the fish-fauna of each habitat is dominated by a particular community of haplochromine species. Besides restrictions to certain habitats most species have limited food-regimes. Together these diets comprise all food categories available (possibly with exception of zooplankton). Morphologically similar species realizing such a wide scala of adaptations are ideal objects for comparative biological research. For this reason haplochromine cichlids have been recently introduced into ethology, ontogeny, physiology, functional morphology and-naturally-ecology. Another recent interest in these fishes concerns their potential economic importance: the overwhelming quantity with which haplochromine cichlids (still) occur, together with an improved fishing gear, make these relatively small fishes a source for fishmeal and human consumption. Regrettably no ecological survey preceded the planning for these extensive fisheries. A major cause for this omission are the difficulties experienced in identifying haplochromine species. These difficulties result partly from the overall morphological similarity and partly from the fact that only half the estimated number of species has been described so far. The importance of identification for both fishery-biology, ecology and other biological research has been the main reason for writing this paper which introduces the techniques applied in the taxonomy of the haplochromine Cichlidae from Lake Victoria. As this taxonomy is mainly based on morphological characters, the paper consequently provides basic information on the anatomy and external aspects of these cichlids. The subtitle refers to the fact that all currently valid species have been described (or revised) by GREENWOOD in a long series of papers mainly intended for the use of taxonomists. The present introduction has been explicitly written for students unfamiliar with the morphology and taxonomy of haplochromine fishes. After a short review of the problems related to haplochromine taxonomy, there

Ecological investigations on the haplochromine Cichlidae from the Mwanza Gulf of Lake Victoria revealed that more than 140 species are living in the habitats fished with bottom trawlers (i.e. all major habitats except rocky bottoms, dense plant stands and very shallow water). These species can be classified into 9 trophic groups. The phytoplankton/detritus eaters and the zooplanktophages (both belonging to the smaller species) form the dominant group in the sublittoral waters with a mud bottom, while insect eaters dominate in shallower water, especially over sand. Most haplochromine species appear to be strongly habitat-restricted throughout life. Breeding of the bulk of the haplochromine species (phytoplankton/detritus eaters, zooplanktophages and some insectivores) in the sublittoral and littoral waters with a mud bottom appears to be seasonal. Spawning takes place at the end of the rainy season. However, some species of the littoral sand habitat breed throughout the year. A discussion is given of the factors by which the seasonal breeding pattern might be imposed. For an optimal trawl fishery recommendations based on the present data are discussed.

This paper deals with the jaw mechanism of Haplochromis elegans, a generalized 1 Haplochromis 2 species. The central issues are the kinematics and statics of the mechanism and the way these are influenced by its proportions. These proportions change during growth and differ in related species. A mathematical computer model is formulated to deal with the kinematics and the statics of the mechanism. A calculation procedure is developed to determine the importance of the position of anatomical points in the mechanism for force-transmission during biting. It is also possible to change the position of all relevant anatomical points gradually and thereby improve the whole mechanism for the function of biting. In this way a prediction is made about the proportions expected in a powerful biting haplochromine species such as H. nigricans. The predictions made are correct in six of the seven specialized proportions of H. nigricans. A simplified kinematical model is presented which demonstrates the essence of protrusion in cichlid fishes and in many other acanthopterygian fishes. The differences in proportions of an adult and a first free-swimming stage of H. elegans are evaluated with the computer model. It appears that some proportions are more favourable for biting in the young stage, others are unfavourable due to the relative size of the eye.

The ecology and taxonomy of the haplochromine cichlids from the Mwanza Gulf of Lake Victoria (East Africa) have been studied by the Haplochromis Ecology Survey Team (HEST). The research area and the fishing techniques are described as basic information for following publications. Taxonomic studies resulted in the recognition of 150+ new species. The results of the ecological research on these species-including factors which influence species distribution, breeding and migration-are summarized.

Understanding why some evolutionary lineages generate exceptionally high species diversity is an important goal in evolutionary biology. Haplochromine cichlid fishes of Africa’s Lake Victoria region encompass >700 diverse species that all evolved in the last 150,000 years. How this ‘Lake Victoria Region Superflock’ could evolve on such rapid timescales is an enduring question. Here, we demonstrate that hybridization between two divergent lineages facilitated this process by providing genetic variation that subsequently became recombined and sorted into many new species. Notably, the hybridization event generated exceptional allelic variation at an opsin gene known to be involved in adaptation and speciation. More generally, differentiation between new species is accentuated around variants that were fixed differences between the parental lineages, and that now appear in many new combinations in the radiation species. We conclude that hybridization between divergent lineages, when coincident with ecological opportunity, may facilitate rapid and extensive adaptive radiation. Cichlids underwent a rapid diversification in the Lake Victoria region, expanding to more than 700 species within 150,000 years. Here, Meier and colleagues show that an ancient hybridization between two divergent cichlid lineages generated high genetic diversity that facilitated the rapid radiation.