Intestinal coiling pattern in the epilithic algal-feeding cichlids (Pisces, Teleostei) of Lake Tanganyika, and its phylogenetic significance

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.     

Recruitment of juvenile mbuna (Pisces: Cichlidae) to experimental rock shelters in Lake Malawi,Africa

Synopsis Mbuna are species of small cichlids that inhabit the rocky shoreline of Lake Malawi. They are mouthbrooders and do not guard their young. Recruitment to the community first occurs when the female deposits free-swimming young, approximately 11 mm standard length, among the rocks. Juvenile mbuna recruit to any refuge in the rock habitat and in this study, small rock shelters were monitored daily to follow the recruitment and subsequent persistence of young. Initial mortality rate was high; less than 10% of the fish survived more than 3 weeks after deposition by the female. At the two locations studied, recruitment was greater at West Thumbi Island (11 fish per day) than at Otter Point (8 fish per day). However, fewer recruits persisted as residents at Thumbi Island because mbuna young at Thumbi were capable of excluding subsequent recruits to their shelter. Similar priority effects were not observed at Otter Point. Mbuna lack pelagic stages in the life-cycle and the species composition of local adult assemblages is an important determinant of the number and type of subsequent recruits. Priority effects may help maintain stochastic influences on recruitment success and reduce the importance of deterministic processes that are directly linked to community structure.     

The feeding habits of a group of herbivorous rock-dwelling cichlid fishes (Cichlidae: Perciformes) from Lake Malawi,Africa

Synopsis The feeding; habits of a group of tropical herbivorous rock-dwelling cichlid fishes from Lake Malawi, Africa, are investigated using stomach content analyses. The various species fed selectively on the periphyton of the rocky shores. Blue-green alga of the genus Calothrix was the most common item ingested by the group. Diatoms (Chrysophyta) also were abundant food items. Discriminant analysis showed that dietary items were good variables to identify species. Interspecific dietary differences showed a continuum from those species feeding primarily on Calothrix to those feeding primarily on diatoms. Algal resources exhibit distinct patterns of spatial variation. Diet was correlated with foraging behavior and trophic morphology. Interspecific differences in diet could possibly facilitate ecological coexistence among various species. Such coexistence would contribute to the maintenance of the high diversity fish faunas characteristic of the Great Rift Lakes of Africa.     

Morphological analyses of the neurocranium of a group of rock-dwelling cichlid fishes (Gichlidae: Perciformes) from Lake Malawi, Africa

Variation in the size and the shape of neurocrania of a group of rock-dwelling cichlid fishes (mbuna; from Lake Malawi, Africa was analysed using principal components and regression analyses on a set of 24 neurocranial measurements of 86 individuals from 11 species. The results reveal effective morphological discrimination between species. Most of the structural variation between species demonstrates positive allometry and represents size-dependent species differences. Thus, morphological differentiation in these fish may be largely the result of heterochronic changes in relative growth rates. The vomerine region, however, exhibited shape differentiation. Distinct groupings, based on vomer shape, are identified. Foraging behaviour and diet are found to be correlated with this region of the neurocrania. The correlation of the shape of the vomer and fine-scale resource partitioning suggests that this structure may be important in the evolutionary success of the group. Also, most structural shape variation in neurocranial morphology is associated with structural variation in buccal jaws.     

Local adaptations in populations of rock-dwelling haplochromines (Pisces:Cichlidae) from southern Lake Victoria

The radiation of cichlid fishes in the African great lakes is often described as adaptive, because, at a superficial level, cichlid fishes seem adapted to the ecological niches they occupy. However, adaptedness has rarely been studied. We''ve investigated to what extent island populations of three species of the rock-dwelling genus Neochromis, endemic to Lake Victoria, are adapted anatomically to exploit locally abundant resources. Specifically, we asked whether different resource environments were reflected in differences in the feeding apparatus, both within species and between species. In populations of two specialized biters, the algae scrapers N. rufocaudalis and N. omnicaeruleus, the biting force of the lower jaw increased with increasing amount of items that require biting in the diet. N. greenwoodi is a less specialized biter; we found differences between two populations in the hyoid position and in the premaxilla that enhance suction feeding. These adaptations were related to the amount of items requiring suction. Comparing across three sympatric pairs of species, in each case different diets were reflected in differences in anatomy.     

Midwater spawning inHaplochromis chrysonotus (Boulenger) (Teleostei: Cichlidae) in Lake Malawi

Synopsis Haplochromis chrysonotus, a semipelagic shoaling cichlid from Lake Malawi, has been observed spawning in open water up to ten metres above the substratum. It is suggested that open water spawning without the establishment of a substratum-based territory eliminates competition with other species for breeding space and that it may be a stage in the evolution of a totally pelagic mode of life.     

Description of a commercially important pelagic species of the genus Diplotaxodon (Pisces: Cichlidae) from Lake Malawi, Africa

A new species of pelagic haplochromine cichlid of the genus Diplotaxodon is described from Lake Malawi, Africa. The species, which attains a size of 14cm s. L., feeds mainly on zooplankton, shows no sexual dimorphism in size or body proportions, breeds throughout the year and lives at depths of 20 to at least 120 m. Approximately 600 tonnes of the species were caught by trawlers in 1990–1991, in the south–eastern arm of the lake alone. It appears that this species is a major component of the pelagic community, and occupies an ecological role similar to that of the clupeid Limnothrissa miodon in Lake Tanganyika.     

Ecomorphology of retinal structures in zooplanktivorous haplochromine cichlids (Pisces) from Lake Victoria

Synopsis 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.     

A revision of the genus Labidochromis (Teleostei: Cichlidae) from Lake Malawi

The diagnosis of the genus Labidochromis is revised to include species with bicuspid outer teeth. Sixteen species, of which 13 are new, are described and illustrated and the validity of five others is discussed. The interrelationships between members of the genus and the relationship of the genus to other genera are discussed. No clearly defined sister group to the genus has been found either within or outside the Lake Malawi cichlid species flock. A key based on the coloration of known species is included.     

Feeding-site utilization in three sympatric species of Petrotilapia (Pisces, Cichlidae) from Lake Malawi

Three sympatric sibling species of Petrotilapia , with similar dietary and macrohabitat requirements, occur near Monkey Bay, Lake Malawi. Males and females of all three species fed selectively on the rocky shores. Males utilized less than 6% of the space they defended as a breeding territory for feeding and although interspecific overlap of territories was considerable, only 2.5% of the feeding space used by territorial males was shared. Males primarily utilized rich food patches which occurred within the territories of highly aggressive Pseudotropheus species, whereas females tended to feed in undefended areas. Although Petrotilapia species are not highly aggressive fishes, there was a well-defined social dominance hierarchy amongst them and it is suggested that feeding-site utilization is dependent on social rank. Inter-and intraspecific differences in feeding-site utilization probably facilitate species coexistence and thus contribute to the maintenance of the high species diversity which is a characteristic of the ichthyofauna of Lake Malawi.     

Sexual selection,reproductive behavior,and speciation in the mbuna species flock of Lake Malawi (Pisces: Cichlidae)

Synopsis 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 endemicPseudotropheus 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.     

Evidence for lacustrine breeding by sanjika Opsaridium microcephalum (Teleostei: Cyprinidae) in Lake Malawi

Three species of Opsaridium occur in the Lake Malawi catchment. The kabyabya Opsaridium tweddleorum is a small species restricted to inflowing rivers and streams, the mpasa Opsaridium microlepis is a large lake-dwelling species that ascends the lower reaches of inflowing rivers during the rains to spawn, and the sanjika Opsaridium microcephalum has riverine, potamodromous and lake spawning populations. Evidence for sanjika spawning in the lake itself, rather than just in rivers, is presented here in the form of observations of courting behaviour by fully mature males and females on exposed rocky shores, together with the presence of pin-head fry in areas remote from any inflowing streams during the dry season.     

A gular plate in Pterothrissus (Pisces, Teleostei)

A gular is reported in Pterothrissus belloci Cadenat and P. gissu Hilgendorf (Albuloidei, Pterothrissidae).     

Phylogeny,taxonomy, and evolution of Neotropical cichlids (Teleostei: Cichlidae: Cichlinae)

Despite recent progress on the higher‐level relationships of Cichlidae and its Indian, Malagasy, and Greater Antillean components, conflict and uncertainty remain within the species‐rich African, South American, and Middle American assemblages. Herein, we combine morphological and nucleotide characters from the mitochondrial large ribosomal subunit, cytochrome c oxidase subunit I, NADH dehydrogenase four, and cytochrome b genes and from the nuclear histone H3, recombination activating gene two, Tmo‐4C4, Tmo‐M27, and ribosomal S7 loci to analyse relationships within the Neotropical cichlid subfamily Cichlinae. The simultaneous analysis of 6309 characters for 90 terminals, including representatives of all major cichlid lineages and all Neotropical genera, resulted in the first well‐supported and resolved generic‐level phylogeny for Neotropical cichlids. The Neotropical subfamily Cichlinae was recovered as monophyletic and partitioned into seven tribes: Astronotini, Chaetobranchini, Cichlasomatini, Cichlini, Geophagini, Heroini, and Retroculini. Chaetobranchini + Geophagini (including the “crenicichlines”) was resolved as the sister group of Heroini + Cichlasomatini (including Acaronia). The monogeneric Astronotini was recovered as the sister group of these four tribes. Finally, a clade composed of Cichlini + Retroculini was resolved as the sister group to all other cichlines. The analysis included the recently described ?Proterocara argentina, the oldest known cichlid fossil (Eocene), which was placed in an apical position within Geophagini, further supporting a Gondwanan origin for Cichlidae. These phylogenetic results were used as the basis for generating a monophyletic cichline taxonomy. © The Willi Hennig Society 2008.     

Distribution and breeding biology of offshore cichlids in Lake Malawi/ Niassa

Synopsis Lake Malawi/Niassa is the second largest rift valley lake in Africa, with an area of 28 800 km², and an average and maximum depth of 292 m and>700 m, respectively. The lake is well known for the great diversity of fish occurring in the inshore zone. However, the offshore fish community is poorly documented. To rectify this, regular sampling was undertaken over two years, using trawl and gillnets at six offshore locations. This paper reports on the species composition, spatial distribution and breeding biology of the dominant cichlids species from the offshore pelagic zone. Cichlids formed approximately 88% of the offshore fish biomass. Most abundant were two species of zooplanktivores in the genus Diplotaxodon that made up 71% of the offshore fish biomass. An undescribed species, given the cheironym D. bigeye, was mainly found at a depth of 220 m during the day, but moved into near surface waters at night when the moon was full. This species was absent from the shallow regions of the lake. The most abundant offshore species was D. limnothrissa, which was distributed evenly throughout the lake to depths of 220 m. A less common offshore zooplanktivore was Copadichromis quadrimaculatus that formed 5% of the biomass and was confined to the upper 100 m of the water column. The main piscivores were in the genus Rhamphochromis and formed approximately 10% of the offshore fish biomass. The two dominant taxa were R. longiceps and the large Rhamphochromis group, and both were more common in the southern half of the lake. The former occurred mainly in the upper 100 m of the water column and the latter mainly at depths of 100–150 m. The length at maturity and fecundity for the dominant offshore species were estimated and seasonal breeding cycles determined from gonad activity and gonado-somatic indices.     

Oxygen concentration profiles in sediments of two ancient lakes: Lake Baikal (Siberia,Russia) and Lake Malawi (East Africa)

Oxygen concentration profiles have been measured, by means of with microelectrodes in sediments of Lake Baikal and Lake Malawi, along transects allowing to give a survey of two major ancient Rift lakes: Lake Baikal (Eastern Siberia) and Lake Malawi (East Africa), along depth transects in the constitutive basins of the lakes and/or of relevant depths with regard to oxygen (including including the deepest point, 1680 m, in Lake Baikal). Sediment oxygen penetration depths (SOPs) display very different patterns, depending on the lake in the two lakes. In Lake Baikal, SOPs are variable, show no significant relationship with bathymetric depth and are surprisingly deep on Akademichesky ridge (> 50.0 mm), emphasizing the distinctive feature of this region in the lake. While the Selenga river is an important source of eutrophication, the similarity of SOP-values in the Selenga shallow with those of most other sites suggests either a dilution of organic material by allochthonous matter, or a strong south-to-north transport of particles. In Lake Malawi, available oxygen is restricted to a maximum of three millimetres of the sediment, and there is a negative relationship with bathymetric depth, as a result of a steady decline of oxygen concentration with depth through the water column. Amongst the few parameters known to affect SOPs, the oxygen consumption by the sediment seems the most significant in both lakes. SOP-values furthermore confirm differences in the trophic status of Baikal and Malawi, respectively. The importance of oxygen as a factor likely to create ecological segregation for benthic organisms is discussed. Lake Malawi offers possibilities of bathymetric segregation but no vertical segregation in the sediment. In contrast, no bathymetric segregation related to oxygen is possible in Lake Baikal, but vertical segregation in the sediment is very likely. This revised version was published online in July 2006 with corrections to the Cover Date.     

The growth of Tilapia mossambica Peters (Pisces: Cichlidae) in Lake Sibaya, South Africa

The scales of Tilapia mossambica Peters * from Lake Sibaya show clear rings formed by broken, widely-spaced circuli in the anterior field. In order to determine the rate and time of scale ring formation, the number of circuli in the marginal increment was determined. Five scales from the pectoral region of 2223 fishes caught at regular intervals over two years were examined. When plotted as histograms, the number of circuli in the marginal increment showed a sharp movement to the left in September–October and again in January, indicating that the rings were formed during these months in the majority of fish examined. Pre- and postbreeding feeding migrations, and increases in condition factor, were associated with scale ring formation. Otoliths and opercula were also examined for age determination. Annual length increments were calculated for 450 T. mossambica collected throughout the year, and growth curves plotted. T. mossambica from Sibaya reach maturity after one year at a standard length of about 8 cm in females, and after two years at 10 cm in males. The breeding population had a standard length mode of 11–12 cm in females and 17 cm in males. The maximum final size was about 24 cm.