Haplochromine Cichlids Research Articles

Changes in the diet of Nile perch, Lates niloticus (L), in the Mwanza Gulf, Lake Victoria

Samples of Nile perch (Lates niloticus L.) were collected for stomach analysis from trawl catches conducted in the Mwanza Gulf from September 1986 to September 1988. Initially haplochromine cichlids formed the main food item for the Nile perch. Despite their decline, haplochromines still formed the major part of its diet in 1986.

Explosive speciation and adaptive radiation of haplochromine cichlids from Lake Victoria: An illustration of the scientific value of a lost species flock

(1992). Explosive speciation and adaptive radiation of haplochromine cichlids from Lake Victoria: An illustration of the scientific value of a lost species flock. SIL Communications, 1953-1996: Vol. 23, No. 1, pp. 101-107.

Egg Mimics in Haplochromine Cichlids (Pisces, Perciformes) from Lake Victoria

AbstractAn ecomorphological explanation is given of the anal spots of haplochromine cichlids from Lake Victoria. Anal spots are ovoid orange‐yellow spots on the anal fins of these fishes. The possible roles of sexual selection and predation as determinants of the form of these spots are discussed. Evidence is given that the anal spots are egg mimics and thus examples of intra‐specific mimicry. Mimicking an egg to stimulate sexually active females presumably is an important demand on the form of the anal spots. However, no positive correlation was found between anal spot size and egg size. Light intensities of the habitat of the species investigated showed a negative correlation with anal spot size. In contrast to this, egg size did not show a negative correlation with light intensities. It is suggested that, besides mimicry, at least one more demand is involved in determining spot size: that of being conspicuous. Conspicuousness is likely to have a positive impact (benefits) on courting conspecific females, but a negative one (costs) with regard to predators who hunt visually for either adults or eggs. The actual appearance of anal spots may be a compromise. This may explain the mismatch between egg size and spot size in many species. Qualitative evidence is presented that predation pressures on adult haplochromines exerted by visually hunting predators are relatively high in lighter habitats, viz. near the rocks and near the surface. An alternative hypothesis that spots in dark surroundings cannot be seen unless they are supra‐normal is discussed.

Captive breeding for the conservation of cichlid fishes

Cichlid fishes are by far the largest familial group of endangered vertebrates, especially the haplochromines. This paper concerns the organization and management of captive breeding of haplochromine cichlids. The setting up of a small‐scale laboratory programme for the conservation of endangered species is described in terms of funding, staffing, installation and livestock husbandry. Breeding is discussed in the context of the selection of broodstock, basic reproductive biology, rearing, disease, pathological disorders and the arrangements necessary for the transfer and documentation of progeny. There are already indications in Africa and elsewhere that the dramatic decline and demise of cichlid taxa in Lake Victoria will not be an isolated phenomenon. There is no prospect that the captive breeding of cichlids can alone resolve such large‐scale problems in fisheries management and ecology, or prevent the loss of taxa in nature. Nevertheless, captive breeding provides conservation options which are otherwise limited or unavailable regarding the saving of individual ‘heritage’ species, restocking to the wild, fundamental laboratory research and, finally, public education on the grave issue of actual and prospective mass extinctions of cichlids and other rare fishes.

Ecological Segregation in Zooplanktivorous Haplochromine Species (Pisces: Cichlidae) from Lake Victoria

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.

Changes in the prey ingested and the variations in the Nile perch and other fish stocks of Lake Kyoga and the northern waters of Lake Victoria (Uganda)

The fish stocks of Lakes Kyoga and Victoria have changed since Nile perch, Lates niloticus (L.), was introduced, and this is reflected in the prey ingested by the predator. Initially, haplochromine cichlids constituted the main prey of most sizes of Nile perch. As the stocks of these have declined, Caridina nilotica (Roux) and Anisopteran nymphs have become the dominant food of the juveniles, while Rastrineobola argentea (Pellegrin), juvenile Nile perch and Oreochromis niloticus (L.) have become the main food of larger Nile perch. Apart from R. argentea, most of the native fish species of these lakes have disappeared. The stocks of Nile perch in Lake Kyoga, to which it was introduced earlier than to Lake Victoria, have declined after dominating the fishery since 1965. and have been superseded by O. niloricus. an introduced herbivore. Similar changes are now occurring in Lake Victoria. The Nile perch might not maintain the high yield realized in the two lakes when haplochromines were abundant. It is therefore necessary to exercise caution with high and long‐term investments aimed specifically at developing the Nile perch fishery.

On the possible role of egg mimics in speciation

Sexually active male haplochromine cichlid fishes possess pronounced yellow ovoid spots on the anal fm, which mimic eggs of the female and have therefore been called egg dummies (Wickler, 1962b). It is thought that divergence in egg dummy characteristics can considerably reduce gene flow and in this way may trigger off reproductive isolation. Two ways in which egg dummy divergence can develop are described. Both mechanisms may have been operating, at the same time and in the same area, in different species, or possibly even in a single species. Firstly, egg dummy divergence can develop in species with accurately mimetic egg dummies if selection pressures on egg characteristics (size, shape) differ in temporarily isolated demes. As soon as egg characteristics diverge, egg dummy characteristics follow. This type of egg dummy divergence leads to reproductive isolation by mimicry. Mimetic isolation is proposed as a term to describe the mechanism. Secondly, egg dummy divergence can develop if selection pressures on the egg dummy characteristics are different in two temporarily isolated demes. Upon secondary contact, this divergence may work as a sexual isolation mechanism, since female mate choice is important in haplochromines. Egg dummy divergence is likely to develop rapidly and, if this happens repeatedly, explosive speciation may result. Apparently, explosive speciation has occurred in haplochromines. Neither of the two models has been properly tested. Some preliminary evidence was found that the second model is valid, but so far there is no evidence in favour of the first model.

The decline of the native fishes of lakes Victoria and Kyoga (East Africa) and the impact of introduced species, especially the Nile perch, Lates niloticus, and the Nile tilapia, Oreochromis niloticus

There has been a decline, and in some cases an almost total disappearance, of many of the native fish species of lakes Victoria and Kyoga in East Africa since the development of the fisheries of these lakes was initiated at the beginning of this century. The Nile perch, Lates niloticus, a large, voracious predator which was introduced into these lakes about the middle of the century along with several tilapiine species, is thought to have caused the reduction in the stocks of several species. But overfishing and competition between different species also appear to have contributed to this decline. By the time the Nile perch had become well established, stocks of the native tilapiine species had already been reduced by overfishing. The Labeo victorianus fishery had also deteriorated following intensive gillnetting of gravid individuals on breeding migrations. L. niloticus is, however, capable of preying on the species which haven been overfished and could have prevented their stocks from recovering from overfishing. L. niloticus is also directly responsible for the decline in populations of haplochromine cichlids which were abundant in these lakes before the Nile perch became established. Even without predation by Nile perch, it has been shown that the haplochromine cichlids could not have withstood heavy commercial exploitation if a trawl fishery had been established throughout Lake Victoria. Their utilisation for human food has also posed some problems. The abundance of the native tilapiine species may also have been reduced through competition with introduced species which have similar ecological requirements. At present, the Nile perch and one of the introduced tilapiine species, Oreochromis niloticus, form the basis of the fisheries of lakes Victoria and Kyoga.

The food of the Nile perch, Lates niloticus (L.), after the disappearance of the haplochromine cichlids in the Nyanza Gulf of Lake Victoria (Kenya)

After the disappearance of the haplochromine species in the Nyanza Gulf of Lake Victoria as a result of predation by Lates niloticus, the latter has turned its attention to aquatic invertebrates and other fish. Changes in the diet of the Nile perch with increase in its size have been observed: young L. niloticus preyed mostly on invertebrates, including crustaceans and various small aquatic insects; large, immature L. niloticus supplemented the invertebrate diet with both young and small fish; adults above 80 cm total length were mainly piscivorous. L. niloticus feeds on fish prey of about one third its own length.The tendency of L. niloticus to switch from one prey item to another, depending on availability, is reported; e.g., in the Nyanza Gulf, the prey diet has shifted from the haplochromine to Caridina nilotica and L. niloticus juveniles.

Enzyme Variation in Haplochromine Cichlid Fishes From Lake Victoria

In the great lakes of Africa, endemism and high rates of speciation are characteristic for some genera within cichlid species flocks. These flocks present novel problems in differentiation and speciation. Much debate has centered around the actual way in which speciation has taken place in the African lakes and in particular whether or not the cichlid flocks provide an example supporting sympatric as opposed to allopatric speciation. To characterize evolutionary changes in some species of the presumed young species flock of Lake Victoria, we studied allozyme variation through electrophoretic analysis of muscle enzymes from 10 haplochromine species. The genetic similarities calculated between the 8 Haplochromis species are very high (genetic identities are all higher than 0.97). Even the monotypic genera Hoplotilapia retrodens and Macropleurodus bicolor are electrophoretically indistinguishable from members of Haplochromis. Based upon the available evidence, the species used here are biologically valid. Therefore it is argued that the very high genetic similarities reported here (and by other authors) are best explained by a very recent separation of the different haplochromine gene pools. This implies that the genetic differences, which did accompany reproductive isolation, involved either regulatory genes or non enzymatic parts of the structural genome. This is in accordance with the accepted views on the dominant factors in cichlid speciation.

Retinal Resolving Power and Sensitivity of the Photopic System in Seven Haplochromine Species (Teleostei, Cichlidae)

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.

Interspecific Fertile Hybrids of Haplochromine Cichlidae (Teleostei) and Their Possible Importance for Speciation

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.

Ecological Differentiation Among the Piscivorous Haplochromine Cichlids of Lake Victoria (East Africa)

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.

An Introduction To Ecological and Taxonomic Investigations On the Haplochromine Cichlids From the Mwanza Gulf of Lake Victoria

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.

Initial Results of the Ecological Survey of the Haplochromine Cichlid Fishes From the Mwanza Gulf of Lake Victoria (Tanzania): Breeding Patterns, Trophic and Species Distribution

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.

Preliminary Comparisons Between the Ecology of the Haplochromine Cichlid Fishes of Lake Victoria and Lake Malawi

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.

Haplochromine Cleaner Fishes: a Taxonomic and Eco-Morphological Description of Two New Species

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.

Revision of Species From the "Haplochromis" Empodisma Group

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.

The Disputed Feeding Behaviour of a Paedophagous Haplochromine Cichlid (Pisces) Observed and Discussed

AbstractAquarium-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.

An Introduction to the Taxonomy and Morphology of the Haplochromine Cichlidae from Lake Victoria

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