Interrelationships of the ostariophysan fishes (Teleostei)

The history of ostariophysan classification is summarized and it is noted that traditional concepts of relationships have never been supported by characters found to be unique to the taxa. We present a new hypothesis of relationships among four of the five major ostariophysan lineages: Cypriniformes, Characiformes, Siluroidei, and Gymnotoidei (Otophysi). Cypriniforms are the sister-group of the remaining three (Characiphysi), and characiforms are the sister-group of siluroids plus gymnotoids (Siluriformes). Placement of the Gonorynchiformes as the sister-group of the Otophysi is supported by additional evidence. Each of the five lineages is monophyletic. Analysis was concentrated upon species thought to be the least specialized within each lineage; choices of these species are discussed. Chanos is determined to be a relatively primitive gonorynchiform morphologically and the sister-group of all other Recent members of the order. Opsariichthys and Zacco are found to be morphologically primitive cypriniforms. We propose that a monophyletic group comprising the Citharinidae and Distichodontidae forms the sister-group of all other characiforms. Within the two families, Xenocharax is the least specialized. We suggest that Hepsetus, the erythrinids, and the ctenoluciids are more derived than the distichodontids and citharinids, and may form a monophyletic group within die characiforms. The traditional hypothesis that Diplomystes is the primitive sister-group of all Recent siluroids is substantiated. Our evidence suggests that Sternopygus is the most primitive gymnotoid morphologically; but rather than being the sister-group of all other gymnotoids, it is the primitive sister-group within a lineage called the Sternopygidae by Mago-Leccia. Previous explanations of otophysan distribution have been based on notions of relationships which are unsupported by the evidence presented herein. Our own analysis of relationships serves primarily to make clear the extent of sympatry, and therefore the probability of dispersal, among the major ostariophysan lineages. The extent of sympatry, together with the widespread distribution of ostariophysans, suggests that the group is older than previously supposed, and our hypotheses of relationships among the characiforms implies that many of the extent characiform lineages evolved before the separation of Africa and South America. Further understanding of ostariophysan distribution must await phylogenetic analysis within each of the five major lineages so that distributions linked with vicariance patterns and dispersal events can be sorted out.     

Sperm of Doradidae (Teleostei: Siluriformes)

Spermatic characteristics were studied in 10 species representing several distinct groups within the catfish family Doradidae. Interestingly, different types of spermatogenesis, spermiogenesis and spermatozoa are correlated with intrafamilial groups previously proposed for Doradidae. Semi-cystic spermatogenesis, modified Type III spermiogenesis, and biflagellate sperm appear to be unique within Doradidae to the subfamily Astrodoradinae. Other doradid species have sperm with a single flagellum, cystic spermatogenesis, and spermiogenesis of Type I (Pterodoras granulosus, Rhinodoras dorbignyi), Type I modified (Oxydoras kneri), or Type III (Trachydoras paraguayensis). Doradids have an external mode of fertilization, and share a few spermatic characteristics, such as cystic spermatogenesis, Type I spermiogenesis and uniflagellate sperm, with its sister group Auchenipteridae, a family exhibiting sperm modifications associated with insemination and internal fertilization. Semi-cystic spermatogenesis and biflagellate spermatozoa are also found in Aspredinidae, and corroborate recent proposals that Aspredinidae and Doradoidea (Doradidae + Auchenipteridae) are sister groups and that Astrodoradinae occupies a basal position within Doradidae. The co-occurrence in various catfish families of semi-cystic spermatogenesis and either biflagellate spermatozoa (Aspredinidae, Cetopsidae, Doradidae, Malapturidae, Nematogenyidae) or uniflagellate sperm with two axonemes (Ariidae) reinforces the suggestion that such characteristics are correlated. Semi-cystic spermatogenesis and biflagellate sperm may represent ancestral conditions for Loricarioidei and Siluroidei of Siluriformes as they occur in putatively basal members of each suborder, Nematogenyidae and Cetopsidae, respectively. However, if semi-cystic spermatogenesis and biflagellate sperm are ancestral for Siluriformes, cystic spermatogenesis and uniflagellate sperm have arisen independently in multiple lineages including Diplomystidae, sister group to Siluroidei.     

Functional morphology of the caudal skeleton in teleostean fishes

The basic function of the caudal skeleton in teleostean fishes is to support the caudal fin, but its parts contribute to this function in somewhat different ways. The main axis for this support is the upturned terminal end of the vertebral column, which ends at the base of the uppermost principal rays. The uroneural struts just ahead of this axis provide support for it. The parts of the caudal skeleton behind and below this upturned axis, the hypurals and parhypural, not only support the caudal rays but also provide a means for differential movements between the upper and lower parts of the fin base. This basic caudal skeleton varies with the position of the fish in the sequence of teleosten evolution, the way in which the fish uses its caudal fin, and to some extent with the shape of the fin.     

Mitochondrial genome of Silurus asotus (Teleostei: Siluriformes)

The complete mitogenome sequence of the Amur catfish Silurus asotus was determined using long PCRs. The genome was 16,528 bp in length and contained 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes, and 1 control region; the gene composition and order of which was similar to most other vertebrates. The overall base composition of the heavy strand is 30.5% A, 25.8% T, 28.0% C, and 15.8% G, with an AT content of 56.3%. The mtDNA sequence of S. asotus shared 93.6% and 90.6% sequence identity with that of Silurus meridionalis and Silurus glanis. This mitogenome sequence data would play an important role in silurid catfish phylogenetics and siluriform catfish systematics in general.     

Nomenclature of cartilaginous elements in the caudal skeleton of teleostean fishes

Nomenclature and abbreviations are proposed for the cartilaginous elements of the caudal skeleton of teleostean fishes. These were developed on the basis of examination of 510 species within 198 families of 31 orders and the determination of the positional relationship between these structures and the bony elements. A review of the most important relative literature is also provided.     

Spermiogenesis and spermatozoal ultrastructure in Trichomycteridae (Teleostei: Ostariophysi: Siluriformes)

Spadella, M.A., Oliveira, C. and Quagio‐Grassiotto, I. 2009. Spermiogenesis and spermatozoal ultrastructure in Trichomycteridae (Teleostei: Ostariophysi: Siluriformes). —Acta Zoologica (Stockholm) 91 : 373–389. Siluriformes comprises the most diverse and widely distributed ostariophysan group, a fish assemblage that includes about three quarters of the freshwater fish of the world. In this study, the ultrastructural characterization of spermiogenesis and spermatozoa in specimens of Copionodontinae (the sister group to all other trichomycterids), Trichomycterinae (a derived trichomycterid group), and Ituglanis (a genus not assigned to any trichomycterid subfamily) is presented. The comparative analyses of the data show that trichomycterid species share six of seven analyzed spermiogenesis characters, reinforcing the monophyly of the group. Analyses of trichomycterid sperm ultrastructure showed that the species studied share the same character states for nine of seventeen characters analyzed. Copionodon orthiocarinatus and Ituglanis amazonicus each share more ultrastructural characters with species of Trichomycterus than with one another. Regarding the families of Loricarioidea, the species of Trichomycteridae share more characters of spermatogenesis, spermiogenesis, and sperm with representatives of the families Callichthyidae, Loricariidae, and Scoloplacidae than with Nematogenyidae, its hypothesized sister group. With the exception of the family Nematogenyidae, the character similarities observed reinforce the monophyly of the superfamily Loricarioidea.     

The composition of the caudal skeleton of teleosts (Actinopterygil: Osteichthyes)

The diural caudal skeleton of teleostean actinopterygians develops phylogeneticaily and ontogenetically from a polyural skeleton. The reduction of the polyural anlage to four, three, two or fewer centra in the adult caudal skeleton takes different pathways in different genera (e.g. compare Elops and Albula) and groups of teleosts. As a result, ural centra are not homologous throughout the teleosts. By numbering the ural centra in a homocercal tail in polyural fashion, one can demonstrate these and the following differences. The ventral elements (hypurals) always occur in sequential series, whereas the dorsal elements (epurals and uroneurals) may alter like the ural centra. The number of epurals, five or four in fossil primitive teleosts, is reduced in other primitive and advanced teleosts, but the same epurals are not always lost. The number of uroneurals, seven in fossil teleosts, is reduced in living teleosts, but it has not been demonstrated that the first uroneural is always derived from the neural arch of the same ural centrum. The landmark in the homocercal tail is the preural centrum I which can be identified by (1) bifurcation of the caudal artery and vein in its ventral element, the parhypural, (2) its position directly caudal to the preural centrum (PU2) which supports the lowermost principal caudal ray with its haemal spine, (3) carrying the third hypaxial element ventral to the course of arteria and vena pinnalis, and (4) by carrying the first haemal spine (parhypural) below the dorsal end of the ventral cartilage plate. The study of the development of the vertebral column reveals that teleosts have different patterns of centrum formation. A vertebral centrum is a complete or partial ring of mineralized, cartilaginous or bony material surrounding at least the lateral sides of the notochord. A vertebral centrum may be formed by arcocentrum alone, or arcocentral arcualia and chordacentrum, or arco-, chorda- and autocentrum, or arcocentral arcualia and autocentrum. This preliminary research demonstrates that a detailed ontogenetic interpretation of the vertebral centra and of the caudal skeleton of different teleosts may be useful tools for further interpretations of teleostean interrelationships.     

Systematics of Tanganyikan cichlid fishes (Teleostei: Perciformes)

The relationships among 53 genera of Tanganyikan cichlid fishes were analyzed based on internal and external morphological features. Comparison of the morphological cladistic tree with a previously proposed classification showed 5 of 12 tribes to be nonmonophyletic. Sixteen tribes were recognized, the changes in classification being that Trematocarini was treated as a junior synonym of Bathybatini; 5 new tribes were established for each of the following genera, Benthochromis, Boulengerochromis, Ctenochromis benthicola, Cyphotilapia, and Greenwoodochromis; Ctenochromis horei was transferred from Haplochromini to Tropheini; and Gnathochromis pfefferi was transferred from Limnochromini to Tropheini. The revised classification was supported by previously proposed molecular trees.     

Phylogenetic relationships among atheriniform fishes (Teleostei: Atherinomorpha)

We present evidence from adult and larval morphology for the monophyly and relationships of Atheriniformes, using other atherinomorphs, mugilids and acanthomorph fishes as outgroups. Atheriniformes is diagnosed by ten characters (larval: short preanal length, single mid-dorsal row of melanophores; adult: vomerine ventral face concave, long Al muscle tendon to lacrimal, two anterior infraorbital bones, pelvic-rib ligament, pelvic medial plate not extended to anterior end, and second dorsal-fin spine flexible). We recognize six families within the order, the hierarchical relationships among which are: (Atherinopsidae (Notocheiridae (Melanotaeniidae (Atherionidae (Phallostethidae, Atherinidae))))). Other major conclusions include: (1) Atherinopsidae (Menidiinae, Atherinopsinae) is diagnosed by 20 characters (e.g. ethmomaxillary ligament attached to palatine dorsal process, ventral postcleithrum with two dorsal rami); (2) Melanotaeniidae (Bedotiinae (Melanotaeniinae (Telmatherinini, Pseudomugilini))) is diagnosed by six characters (e.g. absence of second dorsal-fin spine, sexual dimorphism in body colour and median-fin development, greater body depth); (3) Dentatherina is in Phallostethidae; (4) Atherinidae (Atherinomorinae (Craterocephalinae, Atherininae)) is diagnosed by three characters (lacrimal notch, ventral postcleithrum between first and second pleural ribs, pelvic ventral spine); (5) Atherinidae and Phallostethidae form the Atherinoidea clade diagnosed by seven characters (e.g. interopercle dorsal process absent, dorsal wings of urohyal absent, ventral postcleithrum laminar, pelvic medial plate extended to anterior end, presence of anal plate). Bedotia, Rhodes , and melanotaeniines are shown to be derived within atheriniforms rather than the plesiomorphic sister groups to a paraphyletic 'atherinoid' group. We also demonstrate that groups traditionally placed in Atherinidae (Menidiinae, Atherininae, Atherioninae, etc.) comprise a paraphyletic assemblage.     

The phylogenetic structure of habitat shift and morphological convergence in Asian Clarias (Teleostei, Siluriformes: Clariidae)

Catfishes of the genus Clarias are an important component of the ichthyofauna in Asia and in Africa. Previous studies demonstrated a high diversity in number of species, morphology and habitat, but little was known on the evolutionary processes underlying this diversity. We analysed an original data set of molecular sequences (cytochrome b and 16S genes), habitat and geographic distributions, as well as 29 morphometric measurements taken on 454 specimens of Asian Clarias . Maximum likelihood phylogeny estimation showed an unexpected cryptic diversity due to strong morphological convergence. The patterns of intra- and interspecific phylogenetic divergence are overall explained by geographic isolation. The analysis of habitat transitions with Markovian models showed that Asian Clarias evolved from an ancestor probably living in clear waters. The most frequent transitions occurred between clear and white waters, whereas transitions towards black waters occurred only from clear waters and were rare events. The morphometric analysis suggests a complex pattern of morphological evolution with repeated convergence towards an elongated form in black waters. The phylogeographic patterns of diversification of Asian Clarias agree with previous studies on other groups and the hypothesis that changes in sea level during the Pleistocene had little influence on shaping biodiversity on the Sunda Shelf.     

The uplift of Qinghai-Xizang (Tibet) Plateau and the vicariance speciation of glyptosternoid fishes (Siluriformes: Sisoridae)

Based on the phylogenetic and biogeographical studies of the glyptosternoid fishes in Qinghai-Tibet area, the following hypothesis is proposed: the speciation of this group has a direct relationship with the three uplift intervals of the Qinghai-Tibet Plateau. This process was explained by the theory of vicariance of biogeography. The ancestor of this group was similar toBagarus and/orGlyptothorax, which still have a wide distribution. At the moment when the Tethys sea closed, the Indian tectonic plate collided with the Eurasian tectonic plate, so theGlyptothorax-like andBagarus-like ancestors entered Eurasia and gradually became widely distributed. After the Pleistocene, with the enforced colliding, the gradual uplift of the Qinghai-Tibet Plateau brought about the current water environment, and the Glyptosternoids were generated fromGlyptothorax-like fish under this environment. The presentGlyptosternum, distributed across the Himalayas is the ancestor of Glyptosternoids. In the three uplift intervals of the plateau, the water system of this region was separated gradually andGlyptosternum-like ancestor was isolated in different rivers and evolved into various species. All this resulted in the speciation and formation of the biogeographical pattern of glyptosternoids.     

Spermiogenesis and sperm ultrastructure in ten species of Loricariidae (Siluriformes, Teleostei)

The current study describes the ultrastructural characteristics of spermatogenesis, spermiogenesis, and spermatozoa in specimens of siluriform taxa Neoplecostominae, Hypoptopomatinae, Otothyrinae, Loricariinae, and Hypostominae. Our data show that the characteristics of spermatogenesis and spermiogenesis and spermatozoa ultrastructure of Neoplecostominae are more common to Hypoptopomatinae and Otothyrinae than to Loricariinae and Hypostominae. Furthermore, Loricariinae and Hypostominae have more characteristics in common than with any other group of Loricariidae. These data reinforce the phylogenetic hypotheses of relationships among the subfamilies of Loricariidae. Considering the available data in Loricarioidei, Loricariidae presents ultrastructural characteristics of spermatogenesis and spermiogenesis that are also observed in Astroblepidae, its sister group. However, the most of the characteristics of spermatozoa ultrastructure found in Astroblepidae are also observed in Scoloplacidae, the sister group of a clade composed of Astroblepidae and Loricariidae.     

The ultrastructure of Sorubim lima (Teleostei, Siluriformes, Pimelodidae) spermatogenesis: premeiotic and meiotic periods

The ultrastructure of Sorubim lima spermatogenesis during the premeiotic and meiotic periods was studied. Our observations showed that the germ cells in the cysts are connected by cytoplasmic bridges and the mitotic and meiotic divisions are slightly asynchronous. The first and the last spermatogonial generations differ in the cellular and nuclear volume, nucleolus, chromatin condensation, distribution, size, density, and shape of the mitochondria, presence of 'lamellae anulata', amount and dimension of the 'nuages', and movement of the centrioles. In addition to the nuclear prophase structures, the spermatocyte I shows changes in all other cellular organelles and elongated vesicles appear in the cytoplasm. The accentuated cytoplasmic density and thickened walled vesicles are morphological characteristics that differentiate spermatocytes II from the other germ cells in the cysts of Sorubim lima testis.     

Embryonic growth and trophotaenial development in goodeid fishes (Teleostei: Atheriniformes)

Embryonic growth and trophotaenial development are examined in two species of goodeid fish, Ameca splendens and Goodea atripinnis. During gestation of A. splendens, embryonic dry mass may increase from 0.21 mg at the onset of development to 31.70 mg at term. In G. atripinnis, embryonic dry mass ranges from 0.25 mg at the onset of development to 3.15 mg at term. Increase in mass is primarily due to the uptake of maternally derived nutrients by trophotaeniae, externalized embryonic gut derivatives. Trophotaenial development in both species is divisible into five phases. During the first phase, the anus is formed. The second phase involves dilation of the anus, enlargement of the perianal lips, differentiation of the hindgut absorptive epithelium, and formation of the trophotaenial peduncle. The third phase is characterized by a further marked hypertrophy and lateral expansion of the perianal lips that results in the formation of short trophotaenial processes. During the fourth phase, there is continued outward expansion of the inner mucosal surface of the trophotaenial peduncle that results in its eversion and lobulation. Placental function is established by this phase. Axial elongation and dichotomous branching of trophotaenial processes occurs during the fifth phase. Development of rosette and ribbon trophotaeniae differ in the degree of axial elongation during the fifth and final phase.     

Occurrence of biflagellate spermatozoa in Cetopsidae, Aspredinidae, and Nematogenyidae (Teleostei: Ostariophysi: Siluriformes)

In the present study spermiogenesis was investigated in Cetopsis coecutiens (Cetopsidae), and Bunocephalus amazonicus (Aspredinidae), while spermatozoa ultrastructure was investigated in C. coecutiens, B. amazonicus, and Nematogenys inermis (Nematogenyidae). Aspredinidae and Cetopsidae share a spermatogenesis of the semicystic type, and a particular type of spermiogenesis process not reported in any fish group. In the three species analyzed, spermatozoa are biflagellate with flagella having the classical axoneme formulae (9 + 2). The analysis of thirteen characters showed the presence of eight characters shared by Cetopsidae and Aspredinidae, and six characters shared by Cetopsidae and Nematogenyidae, which may suggest that these three families may be more related than actually hypothesized, comprising a very primitive siluriform lineage originated after Diplomystidae.     

Mitochondrial genomics of ostariophysan fishes: perspectives on phylogeny and biogeography

Abstract Ostariophysi is the second largest superorder within Teleostei. It contains five orders: Gonorynchiformes, Cypriniformes, Characiformes, Siluriformes, and Gymnotiformes. Resolving the higher-level relationships among ostariophysan and related fishes will aid in resolving basal teleostean divergence and provide basis to historical biogeographic analysis of major freshwater fish groups. In this study, we report the complete mitochondrial (mt) DNA sequences for eleven ostariophysan fishes and the results of phylogenetic analyses including these species plus four other ostariophysan and nine non-ostariophysan teleostean fishes. Maximum likelihood and maximum parsimony analyses reconfirmed clupeiforms as the closest relatives of ostariophysans. However, gonorynchiforms were closer to clupeiforms than to otophysans (ostariophysan groups excluding gonorynchiforms), thus raising a question over the current definition of Ostariophysi. The lack of clarity in otocephalan (ostariophysans + clupeiforms) basal relationships implies that such divergence took place over a short period of time. The monophyly of cypriniforms, characiphysans (characiforms, siluriforms, and gymnotiforms), and orders or superorders outside the ostariophysans examined here were conceivably reconstructed. The phylogenetic hypothesis suggests a Pangean origin of otophysans. Within characiphysans, gymnotiforms and siluriforms have independent evolutionary origins and evolutionary histories comparable to or older than that of characiforms. This helps to explain the present geographic distribution of characiphysans.