Cytological and morphological ontogenesis and involution of the thymus in cichlid fishes (Cichlidae,Teleostei)

The ontogenesis and involution of thymus in cichlid fishes was studied with the aim of comparing development in the bottom-spawning species Tilapia zillii and T. tholloni, and in the mouth-brooding species Oreochromis auratus, O. niloticus, O. mossambicus, and Sarotherodon galilaeus. For comparison, data are also given on bottom-spawning Cichlasoma spp. from America and mouth-brooding Pseudotropheus auratus and Aulonocara nyassae from Africa. Developmental changes were followed histologically by means of light and electron microscopy of sections, beginning with embryos 24 h after fertilization, up to 14-year-old specimens of O. auratus. In all these fish, the anlagen of the thymus glands begins from the third and fourth gill pouches, and their development shows a high correlation with the pace of general organogenesis, which differs greatly in the bottom-spawning and mouth-brooding cichlids. In juveniles of bottom-spawners of 20–40 mm total length and in mouth-brooders of 40–60 mm total length, three cell types are present in the thymus: thymocytes, with large, dense nuclei; epitheliocytes, with long cell extensions containing bundles of tonofibrils; and reticulocytes, with short, granulated cell extensions. Hassall's corpuscles start to develop in larvae of T. zillii at 20–35 mm total length, and in specimens of 40 mm and more total length the corpuscles are typical, formed by inner and outer rings of epitheliocytes. At 30–45 mm total length, cell debris starts to accumulate in the interior of the corpuscles as an early sign of regression. As involution continues, macrophages accummulate within and around the Hassall's corpuscles. The epitheliocyte rings are eventually completely broken down. Isles of thymocytes persist in tilapias from the age of 1–14 years, but most of the thymus volume is occupied by blood lacunae and pigmented macrophage aggregations. The morphology is similar in the mouth-brooding species Pseudotropheus beginning at 1.5 years of age. © 1995 Wiley-Liss, Inc.     

Molecular phylogeny and biogeography of the Neotropical cichlid fish tribe Cichlasomatini (Teleostei: Cichlidae: Cichlasomatinae)

We have conducted the first comprehensive molecular phylogeny of the tribe Cichlasomatini including all valid genera as well as important species of questionable generic status. To recover the relationships among cichlasomatine genera and to test their monophyly we analyzed sequences from two mitochondrial (16S rRNA, cytochrome b) and one nuclear marker (first intron of S7 ribosomal gene) totalling 2236 bp. Our data suggest that all genera except Aequidens are monophyletic, but we found important disagreements between the traditional morphological relationships and the phylogeny based on our molecular data. Our analyses support the following conclusions: (a) Aequidens sensu stricto is paraphyletic, including also Cichlasoma (CA clade); (b) Krobia is not closely related to Bujurquina and includes also the Guyanan Aequidens species A. potaroensis and probably A. paloemeuensis (KA clade). (c) Bujurquina and Tahuantinsuyoa are sister groups, closely related to an undescribed genus formed by the 'Aequidens'pulcher-'Aequidens'rivulatus groups (BTA clade). (d) Nannacara (plus Ivanacara) and Cleithracara are found as sister groups (NIC clade). Acaronia is most probably the sister group of the BTA clade, and Laetacara may be the sister group of this clade. Estimation of divergence times suggests that the divergence of Cichlasomatini started around 44Mya with the vicariance between coastal rivers of the Guyanas (KA and NIC clades) and remaining cis-andean South America, followed by evolution of the Acaronia-Laetacara-BTA clade in Western Amazon, and the CA clade in the Eastern Amazon. Vicariant divergence has played importantly in evolution of cichlasomatine genera, with dispersal limited to later range extension of species within genera.     

Structure and development of first-generation teeth in the cichlid Hemichromis bimaculatus (Teleostei, Cichlidae)

In order to build a reference system to assess results of ongoing in vitro experiments on the study of epithelial-mesenchymal interactions during odontogenesis in actinopterygians, we have chosen to study the first-generation teeth of the cichlid Hemichromis bimaculatus from initiation until attachment both at the light and transmission electron microscopical level. Although their development follows the general pattern of teleost tooth formation, first-generation teeth show peculiarities compared with later tooth generations, including their size, bare emergence from the epithelium, absence of dentinal tubules and of nerves and capillaries in the pulp cavity, and organization of the outer dental epithelium. Four developmental stages (a to d) prior to attachment (stage e) have been distinguished. The oral epithelium invaginates into the underlying mesenchyme (stage a) and is later folded to form a bell-shaped dental organ (stage b) without any primordial thickening, or any other morphological indication of imminent invagination. Then, the collagenous enameloid matrix is laid down, most probably by the odontoblasts (early stage c), soon followed by predentine deposition and the beginning of enameloid mineralization (late stage c). With ongoing dentinogenesis, the enameloid matrix matures (stage d), i.e. the organic constituents are removed and the matrix further mineralizes. Finally (stage e), an annular collar of attachment bone is deposited to fix the tooth onto the underlying bone.     

Comparison of testes structure,spermatogenesis, and spermatocytogenesis in young,aging, and hybrid cichlid fish (Cichlidae,Teleostei)

Testis structure, spermatogenesis, and spermatocytogenesis were compared in 13 species of cichlid fishes, belonging to the subfamilies Haplochrominae and Tilapinae. The species studied were either mouth brooders, in which fertilization occurs mostly inside the mouth of the brooding fish, or substrate brooders, whose eggs adhere to a substrate over which the sperm is ejaculated. In this study, the embryogenesis of testes anlagen and sperm production was followed in embryos and in fish up to 15 years old, as well as in hybrids of the two subfamilies. In cichlids, the testes are of the unrestricted type and primary spermatogonia develop along the entire length of the developing sperm tubule. The first primary spermatogonia are observed in the testes anlagen 2-5 days after fertilization and they continue to develop in cysts formed by the enveloping Sertoli cells and the intertubular elements. The dimensions of such primary and secondary spermatocysts are correlated with the number of spermatogonia they contain and the corresponding number of mitotic multiplications. The largest mature cysts attained 300 microm, and contained 2,200-2,400 spermatids in the mouth-brooding species and 2,600-3,200 in the substrate-brooding species. Despite the fact that in such cysts cytoplasmic bridges connect only the isogamete spermatids, the maturation of all cells and consequent spermiation is synchronized. Meristic characters distinguish the sperm of mouth brooders from those of substrate brooders, especially in the number of mitochondria and length of the flagellum. In older fish and hybrids, various changes can be seen in the gametogenic epithelium and intertubular cells. These include thickening of the connective tissue, formation of "yellow" groups of Leydig cells, cell apoptosis and degeneration, and, especially, formation of large spermatogonia, with large, electron-dense nucleoli, that have the cytological characteristics of oocytes. The intra- and interspecific variability of sperm dimensions in the studied cichlids poses an interesting question in the context of sperm competition.     

Teleocichla preta,a new species of cichlid from the Rio Xingu Basin in Brazil (Teleostei: Cichlidae)

Teleocichla preta nov. sp. inhabits the rapids along the Rio Xingu and lower portion of the Rio Iriri. It is the largest species in the genus, reaching 121·3 mm standard length (L_S) while others do not reach more than 87·8 mm L_S. Teleocichla preta is distinguished from all other species of Teleocichla by the unique blackish (in live specimens) or dark brown (preserved specimens) overall colouration of the body, which masks the faint vertical bars or zig‐zag pattern of blotches on the flanks. Teleocichla preta also has a deeper body and a deep laterally compressed caudal peduncle, unlike any other congener, as well as a stout lower pharyngeal tooth plate bearing molariform teeth on its median area.     

Phylogeny and biogeography of cichlid fishes (Teleostei: Perciformes: Cichlidae)

Family level molecular phylogenetic analyses of cichlid fishes have generally suffered from a limited number of characters and/or poor taxonomic sampling across one or more major geographic assemblage, and therefore have not provided a robust test of early intrafamilial diversification. Herein we use both nuclear and mitochondrial nucleotide characters and direct optimization to reconstruct a phylogeny for cichlid fishes. Representatives of major cichlid lineages across all geographic assemblages are included, as well as nearly twice the number of characters as any prior family‐level study. In a strict consensus of 81 equally most‐parsimonious hypotheses, based on the simultaneous analysis of 2222 aligned nucleotide characters from two mitochondrial and two nuclear genes, four major subfamilial lineages are recovered with strong support. Etroplinae, endemic to Madagascar (Paretroplus) and southern Asia (Etroplus), is recovered as the sister taxon to the remainder of Cichlidae. Although the South Asian cichlids are monophyletic, the Malagasy plus South Asian lineages are not. The remaining Malagasy lineage, Ptychochrominae, is monophyletic and is recovered as the sister group to a clade comprising the African and Neotropical cichlids. The African (Pseudocrenilabrinae) and Neotropical (Cichlinae) lineages are each monophyletic in this reconstruction. The use of multiple molecular markers, from both mitochondrial and nuclear genes, results in a phylogeny that in general exhibits strong support, notably for early diversification events within Cichlidae. Results further indicate that Labroidei is not monophyletic, and that the sister group to Cichlidae may comprise a large and diverse assemblage of percomorph lineages. This hypothesis may at least partly explain why morphological studies that have attempted to place Cichlidae within Percomorpha, or that have tested cichlid monophyly using only “labroid” lineages, have met with only limited success. © The Willi Hennig Society 2004.     

Ontogenesis and functional metamorphosis of the head-kidney in bottomspawner and mouthbrooder cichlid fishes (Cichlidae,Teleostei)

Histological and electron-microscopical studies of the head-kidney ontogenesis in a group of bottomspawner and mouthbrooder cichlid fishes reveal that this organ undergoes three functional and structural stages. At the initial stage, 2–12 days after fertilization, the head-kidney is a filtering organ of two glomeruli and adjacent renal tubules; the second stage, beginning 12–30 days after fertilization, is a functionally mixed one, with the nephron and developing hemopoietic and endocrine, chromaffin, and interrenal cells; during the third stage, which begins 30–60 days after fertilization, the nephron degenerates, and the head-kidney starts functioning solely as a lympho-adrenal organ. With age the interrenal tissue expands, forming fields, especially along the blood vessels. The number of melano-macrophage centers progressively increases within the hemopoietic parts. Data are given on the various cell types, the reticuloendothelial stroma, and the renal part of this organ in various species. The earlier ontogenesis and function of the head-kidney, as thymus and other organs, in bottomspawner larvae compared to the more protected mouthbrooders provide support for earlier free functioning in a dangerous environment. © 1996 Wiley-Liss, Inc.     

Comparative ecology of Serranochromis species (Teleostei: Cichlidae) in the Upper Zambezi River floodplain

The Upper Zambezi River drainage of Zambia contains six Serrunochromis species belonging to the largemouth, piscivorous subgenus Serranochromis and three smallmouth, invertebrate-feeding species of the subgenus Sargochromis. A survey of the Barotse floodplain and associateddrainages revealed that two species, S. (S.) longimanus (Boulenger) and S. (S.) thumbergi (Castelnau), were uncommon on the floodplain. S. thumbergi appeared to be more abundant in the Kafue, Chobe, and Kabompo rivers than the Upper Zambezi proper. Adults of the three largest species (i.e. S. (S) robustus (Günther), S. (S.) altus (Winemiller & Kelso-Winemiller), and S. (Sar.) giurdi (Pellegrin)) inhabit the main channel of the Zambezi River during low water, whereas most adults of the other four species (i.e., S. (S.) macrocephalus (Boulenger), S. (S.)ungusticeps (Boulenger), S. (Sar.) codringtoni (Boulenger), and S. (Sar.) carlottae (Boulenger)) were collected from lagoons, canals and backwaters. Comparisons of population size structure and gonad condition during the falling water (May-August) and low water (September- December) seasons indicated that the seven common Serranochromis initiate spawning near the end of the low water period. Examination of gonad condition during the pre-spawning period indicated that Serrunochromis attain maturity at the following sizes: S. robustus, males (275-300 mm s.l .), females (250-275 mm); S. macrocephalus, both sexes (150-200 mm); S. altus, males (275-325 mm), females (250-300 mm);S. angusticeps, males (250-275 mm), females (175-225 mm); S. giardi, males (275-300 mm), females (225-250 mm); S. codringtoni, males (150 mm), females (125-150 mm); S. carlottue, males (150-175 mm), females (100-125 mm). Age was estimated from scale annuli comprised of closely spaced circuli that corresponded to the period of rising water (December- March). S. robustus, S. altus, S. angusticeps, and S. giurdi matured at approximately 3 years, and S. macrocephalus, S. codringtoni, and S. curlottae matured at approximately 2 years in the Barotse floodplain. The average numbers of mature oocytes per female were as follows: S. robustus- 1165; S. macrocephalus-810; S. altus-920; S. angusticeps-627; S. codringtoni-580; S. carlottue-362. Fecundity exhibited a weak positive relationship with female size. Analysis of stomach contents showed that interspecific diet overlap was low among both immature and mature size classes of Serrunochromis. Adult size classes of S. robustus fed primarily on small Synodontis catfishes, S. mucrocephalus fed mostly on mormyrid and cichlid fishes, S. altus specialized on mormyrids, and S. angusticeps fed primarily on small cyprinid and characid fishes. The three members of the subgenus Sargochromis consumed mostly invertebrates. Molluscs were the most important item in the diet of S. giardi, and aquatic insects and fish scales were predominant in the diet of S. carlottae. Larger size classes of S. codringtoni consumed large amounts of seeds (Graminaceae). If habitat and diet are considered together, niche separation among Upper Zambezi Serrunochromis species appears to be nearly complete.     

Foraging on patchily distributed prey by a cichlid fish (Teleostei,Cichlidae): A test of the ideal free distribution theory

Cichlid fish (Aequidens curviceps) distributed themselves and allocated their foraging time between two drift food patches in close approximation to the patch profitability ratio, as predicted by the ideal free distribution theory. The fish thereby achieved similar average feeding rates in the two patches, in two of three patch profitability ratio experiments. However, one major assumption of the ideal free model was violated, since individual fish differed in their competitive abilities for limited food resources, which resulted in unequal payoffs among individuals within each patch. Individual variation in feeding rates, and thus in competitive ability, was not related to despotism, but perhaps rather to individual differences in perceptual ability and in the ability to learn which patch was currently the more profitable. The strategy used by the fish to assess patch profitability included sampling available patches. However, individual fish switched (sampled) patches with varying frequency. Sampling had an associated cost, since high-frequency switchers had lower feeding rates on average than low-frequency switchers. Differences in foraging strategy among the fish therefore contributed to the observed in-equality in individual payoffs within patches.     

Description of a new cichlid fish species of the genus Benthochromis (Perciformes: Cichlidae) from Lake Tanganyika

Benthochromis horii , a new cichlid species is described based on 19 type specimens from the deep waters of Lake Tanganyika. It differs from its congeners by having smaller eyes and longer snout (eye length usually shorter than snout length v. equal to or longer than snout length in Benthochromis tricoti and Benthochromis melanoides ), and more dorsal fin rays (total number of spines and soft rays in dorsal fin usually 30 or 31 v. usually 28 or 29 in B. tricoti and B. melanoides ). Large males of the new species differ from those of congeneric species in terms of their body colour pattern and long pelvic fins. This species has been confused with B. tricoti and has been traded as an aquarium fish.     

Phylogeny and species diversity of the genus Herichthys (Teleostei: Cichlidae)

We provide a review of the systematics of Herichthys by evaluating the usefulness of several mitochondrial and nuclear genetic markers together with morphological data. The nDNA next‐generation sequencing ddRAD analysis together with the mtDNA cytochrome b gene provided well‐resolved and well‐supported phylogenies of Herichthys. On the other hand, the nDNA S7 introns have limited resolution and support and the COI barcoding analysis completely failed to recover all but one species of Herichthys as monophyletic. The COI barcoding as currently implemented is thus insufficient to distinguish clearly distinct species in the genus Herichthys that are supported by other molecular markers and by morphological characters. Based on our results, Herichthys is composed of 11 species and includes two main clades (the H. labridens and H. cyanoguttatus species groups). Herichthys bartoni is in many respects the most plesiomorphic species in the genus and has a conflicting phylogenetic position between mtDNA and nDNA markers, where the robust nDNA ddRAD data place it as a rather distant basal member of the H. labridens species group. The mtDNA of H. bartoni is on the other hand only slightly divergent from the sympatric and syntopic H. labridens, and the species thus probably have hybridized in the relatively recent past. The sympatric and syntopic Herichthys steindachneri and H. pame are supported as sister species. The Herichthys cyanoguttatus species group shows two well‐separated basal species (the northernmost H. minckleyi and the southernmost H. deppii) followed by the closely related and centrally distributed species H. cyanoguttatus, H. tepehua, H. carpintis, and H. tamasopoensis whose relationships differ between analyses and show likely hybridizations between themselves and the two basal species as suggested by conflicts between DNA analyses. Several instances of introgressions/hybridizations have also been found between the two main clades of Herichthys.     

Reproductive ecology of a neotropical cichlid fish,Cichla monoculus (Osteichthyes: Cichlidae)

The reproductive ecology of the freshwater fish Cichla monoculus Spix, 1831 (Osteichthyes: Cichlidae) was investigated in the Campo Grande Reservoir, Northeast Brazil. Rainfall, temperature, pH, dissolved oxygen and electrical conductivity of the water were recorded monthly. Fish collected on a monthly basis were measured, weighted, dissected, sexed and the stage of maturation of the gonads were assessed by macro and microscopic means. The semi-arid study region has short spells of rain of 2-3 months duration interspersed with dry seasons. A positive correlation was observed between rainfall and air and water temperatures and conductivity of the water. The study population had an extended spawning season, with peak reproductive activity coinciding with low water temperatures. Males were longer and heavier than females on average and were larger at onset of sexual maturity. The size frequency distributions of the oocytes indicate that C. monoculus is a multiple spawner with an estimated batch fecundity of 3100. Condition factor showed an inverse relationship in relation to gonad size during maturation in both sexes and spent fish were in poor condition. In mature males, lipid stores in the post-occipital cephalic protuberance, a secondary sexual characteristic developed during the reproductive phase, which depleted in spent individuals. The success of this fish is attributed to its reproductive capacity and to the phenotypic plasticity that allows it to adapt to the harsh ecological conditions that prevail in the semi-arid region of Northeast Brazil.     

Microdontochromis rotundiventralis, a new cichlid fish (perciformes: Cichlidae) from Lake Tanganyika

Microdontochromis rotundiventralis, a new species of cichlid fish, is described on the basis of 13 specimens from Nkumbula Island, Lake Tanganyika (Zambia). It is distinct from its only congener,M. tenuidentatus, in having two (rarely one) rows of teeth on both jaws, a rounded distal margin on the pelvic fin, the outermost pelvic fin soft ray length 1.23–1.43 times the innermost ray, a deeper body (depth 26.8–29.1% standard length) and the anal fin with 9 (rarely 8 or 10) soft rays.     

Phylogeny of the Neotropical cichlid fish tribe Cichlasomatini (Teleostei: Cichlidae) based on morphological and molecular data, with the description of a new genus

Phylogenetic relationships among cichlasomatine cichlids were studied using an extensive taxon sampling and both morphological and molecular data sets. A new genus, Andinoacara n. gen. with six species ( A. pulcher-rivulatus group of previous authors) from trans-andean South America and NW cis-andean South America, is described based on results of phylogenetic and diagnosability analyses and tests of alternative topologies Our results demonstrate that cichlasomatine cichlid diversity is divided into five principal lineages composed of eleven genera and three suprageneric clades: the [( Bujurquina , Tahuantinsuyoa ), ( Andinoacara ) (BAT) clade; the ( Cleithracara , ( Nannacara , Ivanacara )] clade (NIC) plus Laetacara and 'Aequidens' hoehnei ; and the ( Aequidens , Cichlasoma ) clade, where Aequidens is paraphyletic to Cichlasoma . Two former Aequidens species are additionally transferred into Krobia ( K. potaroensis , K. paloemeuensis ). 'Aequidens' hoehnei probably represents a unique evolutionary lineage and would thus qualify for a separate generic status. Molecular data are yet not available for this species and its generic status requires further study. Relationships between the three suprageneric clades and between Acaronia and Krobia could not be convincingly resolved with our data set of two mitochondrial (16S and cyt b ) and two nuclear (S7 and RAG1) molecular markers and 96 morphological characters.     

Phylogeographic structure and gene flow in the scale-eating cichlid Perissodus microlepis (Teleostei, Perciformes, Cichlidae) in southern Lake Tanganyika

One of the most fragmented habitats in freshwater lakes is the rocky littoral zone, where the already richly structured habitat is frequently interspersed with more pronounced barriers such as sandy bays, river estuaries and deep slopes. Although habitat fragmentation generally constrains the dispersal of specialized rock-dwelling species, patterns of population structure vary in sympatric taxa due to species-specific traits. In the present study, we examine the phylogeographic and population genetic structure of Perissodus microlepis , a presumptively highly mobile scale-eating cichlid fish endemic to Lake Tanganyika with a lake-wide distribution in the rocky littoral zone and no obvious geographical colour variation. Analysis of the mitochondrial DNA of six populations in the southern end of the lake suggests isolation by distance along rocky shoreline. Across a large muddy bay, a phylogeographic break indicates that environmental barriers restrict gene flow even in this highly mobile species. Restricted dispersal across the bay is not necessarily a consequence of an intrinsic propensity to avoid sand, but may be connected with the association between P. microlepis and other rock-dwelling fish, which the scale-eaters mimic and intermingle in order to be able to approach other fish to rip off scales from their bodies.     

Breeding behavioural pattern of the lake fish Tilapia discolour Gunther (Teleostei, Cichlidae) in captivity

Close observation of the breeding activities of specimens of Tilapia discolour obtained from Lake Bosomtwe and held captive in glass aquaria, a net cage and a pond showed that this species practises substrate-brooding; the eggs were incubated and hatched in prepared nests. However, brief egg-carrying tendencies were observed; both the male and female brood fish carried the eggs in their mouths from the sites of spawning to new sites. Both sexes also made and guarded the nests, incubated the eggs and provided protection to the young fry.     

First description of monogenean parasites in Lake Tanganyika: the cichlid Simochromis diagramma (Teleostei, Cichlidae) harbours a high diversity of Gyrodactylus species (Platyhelminthes, Monogenea)

Lake Tanganyika harbours the most diverse endemic cichlid fish assemblage of Africa, but its monogenean fish parasites have not been investigated. Here we report, for the first time, on the Gyrodactylus parasites in this hotspot of fish biodiversity. Haptor morphometrics and nuclear ribosomal DNA sequences revealed 3 new species on Zambian Simochromis diagramma: Gyrodactylus sturmbaueri n. sp., G. thysi n. sp. and G. zimbae n. sp. Their distinct morphology and strong genetic differentiation suggest that they belong to distant lineages within the genus Gyrodactylus, and phylogenetic reconstructions suggest affinities with other genera of gyrodactylids. Additional U-shaped haptoral plates in G. thysi n. sp. and a second large spine-like structure in the male copulatory organ of G. zimbae seem to represent new features for the genus. Such large diversity on a single host species can probably be explained by host-switching events during the course of evolution, in agreement with the generally accepted concept that ecological transfer is an important aspect of gyrodactylid speciation. Additional parasitological surveys on other host species, covering a broader phylogenetic and geographical range, should clarify the evolutionary history of Gyrodactylidae on cichlids in the African Great Lake and other parts of Africa.     

A new Apistogramma species (Teleostei, Cichlidae) from the Rio Negro in Brazil and Venezuela

Apistogramma diplotaenia sp.n. occurs in the upper and middle Rio Negro. The largest among 186 specimens studied is a 29.2 mm SL male, the largest female is 22.9 mm SL. Distinguishing characters include a unique colour pattern, consisting of two dark bands along the side which converge anteriorly and posteriorly. A comparative osteological study, including other species of Apistogramma and the genera Taeniacara and Apistogrammoides , indicates a progressive forwards loss of infraorbital ossicles and foramina among dwarf cichlids. The long, rod-like interarcual cartilage of Apistogramma, Apistogrammoides and Satanoperca possibly represents a plesiomorphic condition otherwise unknown among cichlids.