Search

Simple Summary: As the most diverse vertebrate group, the unique adaptive expansion of euryhaline fishes is critical to understanding vertebrate evolution. In particular, the high degree of consistency of unique paired appendage structures across the extremely morphologically diverse group of teleost fishes has become a fascinating scientific question. Early teleost fishes provide a critical window into the study of this large taxon. Therefore, this study constructs high-quality chromosome-level genomes of Osteoglossiformes (Chitala ornata). It also explores the genomic features of early teleost fishes and traces the unique genetic basis of pectoral fin evolution in teleost fishes at the molecular level, which provides an important basis for understanding the evolution of the origin of early teleosts. Teleosts are the most prolific vertebrates, occupying the vast majority of aquatic environments, and their pectoral fins have undergone remarkable physiological transformations throughout their evolution. Studying early teleost fishes, such as those belonging to the Osteoglossiformes order, could offer crucial insights into the adaptive evolution of pectoral fins within this group. In this study, we have assembled a chromosomal-level genome for the Clown featherback (Chitala ornata), achieving the highest quality genome assembly for Osteoglossiformes to date, with a contig N50 of 32.78 Mb and a scaffold N50 of 40.73 Mb. By combining phylogenetic analysis, we determined that the Clown featherback diverged approximately 202 to 203 million years ago (Ma), aligning with continental separation events. Our analysis revealed the intriguing discovery that a unique deletion of regulatory elements is adjacent to the Gli3 gene, specifically in teleosts. This deletion might be tied to the specialized adaptation of their pectoral fins. Furthermore, our findings indicate that specific contractions and expansions of transposable elements (TEs) in teleosts, including the Clown featherback, could be connected to their adaptive evolution. In essence, this study not only provides a high-quality genomic resource for Osteoglossiformes but also sheds light on the evolutionary trajectory of early teleosts. [ABSTRACT FROM AUTHOR]

Teleosts are the most prolific vertebrates, occupying the vast majority of aquatic environments, and their pectoral fins have undergone remarkable physiological transformations throughout their evolution. Studying early teleost fishes, such as those belonging to the Osteoglossiformes order, could offer crucial insights into the adaptive evolution of pectoral fins within this group. In this study, we have assembled a chromosomal-level genome for the Clown featherback (Chitala ornata), achieving the highest quality genome assembly for Osteoglossiformes to date, with a contig N50 of 32.78 Mb and a scaffold N50 of 40.73 Mb. By combining phylogenetic analysis, we determined that the Clown featherback diverged approximately 202 to 203 million years ago (Ma), aligning with continental separation events. Our analysis revealed the intriguing discovery that a unique deletion of regulatory elements is adjacent to the Gli3 gene, specifically in teleosts. This deletion might be tied to the specialized adaptation of their pectoral fins. Furthermore, our findings indicate that specific contractions and expansions of transposable elements (TEs) in teleosts, including the Clown featherback, could be connected to their adaptive evolution. In essence, this study not only provides a high-quality genomic resource for Osteoglossiformes but also sheds light on the evolutionary trajectory of early teleosts.

Scleropages formosus (Osteoglossiformes, Teleostei) represents one of the most valued ornamental fishes, yet it is critically endangered due to overexploitation and habitat destruction. This species encompasses three major color groups that naturally occur in allopatric populations, but the evolutionary and taxonomic relationships of S. formosus color varieties remain uncertain. Here, we utilized a range of molecular cytogenetic techniques to characterize the karyotypes of five S. formosus color phenotypes, which correspond to naturally occurring variants: the red ones (Super Red); the golden ones (Golden Crossback and Highback Golden); the green ones (Asian Green and Yellow Tail Silver). Additionally, we describe the satellitome of S. formosus (Highback Golden) by applying a high-throughput sequencing technology. All color phenotypes possessed the same karyotype structure 2n = 50 (8m/sm + 42st/a) and distribution of SatDNAs, but different chromosomal locations of rDNAs, which were involved in a chromosome size polymorphism. Our results show indications of population genetic structure and microstructure differences in karyotypes of the color phenotypes. However, the findings do not clearly back up the hypothesis that there are discrete lineages or evolutionary units among the color phenotypes of S. formosus, but another case of interspecific chromosome stasis cannot be excluded. [ABSTRACT FROM AUTHOR]

The study aimed to determine the fatty acid profile, omegas and lipid quality indeces in commercial cuts of pirarucu (Arapaima gigas) of the slaughter class 11.1 to 14.0 kg. Sample collections were carried out in two fish processing industries located in Rondônia state, Brazil. The experimental design was completely randomized, with processing performed in triplicate. Data were submitted to ANOVA to assess differences between commercial cuts in chemical compositions. If ANOVA appeared statistically significant (α=0.05), the averages were compared by Tukey's test. In the composition of fatty acids, there was a difference (p <0.05) between cuts. Commercial cuts that expressed the highest percentages of SFAs tail fillet 51.2%, of MUFAs fillet mignon 39.8% and of PUFAs deboned cut 20.7%. The indeces prescribed for lipid quality, ΣPUFAs/ΣSFAs, ΣPUFAs (n-6/Σn-3), AI, TI and HH, indicate that commercial cuts have lipid quality. Deboned is the cut with the highest PUFA fatty acid content, with the highest values of Omega 3, 6, 7 and n-9 being also expressed. Nutritional information is important for the processes of conservation and processing, development of new products on the market, as well as guiding the form of preparation, thus providing commercial security for different market niches. [ABSTRACT FROM AUTHOR]

A study was carried out from October, 2020 to September, 2021to investigate the diversity of fishes and the conservation status of Chittaura Jheel (Bahraich), Uttar Pradesh. During the study period, 38 fish species belonging to 28 genera, 14 families and 7 orders have been identified. The order Cypriniformes was found the dominated order with 15 species(39.47%) followed by Siluriformes 10 species (26.31%), Perciformes 4 species (10.52%), Ophiocephaliformes 4 species (10.52%), Synbranchiformes2 species (5.26%), Osteoglossiformes 2 species (5.26%) and Clupiformes 1 species (2.63 %), The present investigation showed that the wetland, Chittaura Jheel possesses rich fish biodiversity but proper conservation measures are required to maintain sustainability and richness of the fish species diversity of that wetland of U.P. According to IUCN, 30 were enlisted as Least Concern (LC), 2 species as near endangered (NE), 3 species as near threatened (NT), 2 listed as Endangered (EN) and 1 species was listed as Vulnerable (VU). There is a need of conservation of fish diversity of this natural wetland. The pressure is increasing day by day due to increasing population, leading to loss of fish diversity hence identifying the problem and making a better management plan is the way for conservation of the fish diversity of the Chittaura Jheel, a wetland of Bahraich district of Uttar Pradesh. [ABSTRACT FROM AUTHOR]

ABSTRACT Pirarucu is one of the main fish species for the development of aquaculture in the Amazon. In this study, the optimal feeding frequency for juvenile pirarucu was assessed based on growth and feed efficiency. Juvenile pirarucu weighing ca. 80 g were fed once, twice, three or four times daily until apparent satiation for 63 days. Fish fed three or four times per day presented higher growth, feed intake, and fat body content than those fed once or twice per day. There was no significant difference for feed conversion ratio, and protein and energy retention rates among treatments, suggesting that increased feeding frequency did not affect feed utilization efficiency. Mean feed intake per meal was higher when fish were fed once per day, possibly causing hyperphagic behavior. Results suggest that feeding three times per day was sufficient to secure adequate feeding and growth of juvenile pirarucu.

Osteoglossomorpha, an ancient Teleostei group, exhibits many ancestral structural features. Herein, we describe the diversity in morphology of olfactory organs of air‐breathing Pantodon buchholzi, Arapaima gigas, and Gymnarchus niloticus in terms of adaptations to short ventures out of water and compare the results with the water‐breathing Osteoglossum bicirrhosum. We demonstrate the presence of olfactory rosettes within the olfactory chamber in all studied species and additionally a peculiar cudgel‐shaped structure in P. buchholzi. The typical olfactory rosette with centrally located elongate median raphe and two rows of olfactory lamellae was found only in P. buchholzi. In A. gigas, the olfactory lamellae arranged in semicircular manner were merged to small median raphe. Osteoglossum bicirrhosum and G. niloticus lacked median raphe, while the olfactory lamellae were ordered nearly parallel or circular, respectively. Olfactory epithelium lining the olfactory lamellae was unfolded only in P. buchholzi and G. niloticus. In contrast, in O. bicirrhosum and A. gigas convexities formed by nonsensory cells and concavities made by the sensory component were observed. Among the olfactory sensory neurons, ciliated and microvillus neurons were found in all studied species. Crypt‐like cells were noted only in P. buchholzi, whereas rod‐like cells were unique for A. gigas. The substantial morphological variation of the olfactory organ structure and ultrastructure in the studied osteoglossiforms may be explained by the early division of Osteoglossomorpha within Teleostei and long‐term, independent evolution within the families. [ABSTRACT FROM AUTHOR]

The structure of a fish population is determined by the equilibrium between growth, recruitment and total mortality. But, there is paucity of information on the growth and mortality of Mormyrus rume in Nigeria. Therefore this study is needful to determine its population parameters, with a view of evolving management strategies for its sustainable exploitation. Estimates of population parameters of Mormyrus rume were obtained from length-frequency data of 836 individuals collected monthly for a period of 24 months from January 2017 to December 2018. The estimated growth parameters were: asymptotic length (L8) was 100.8cm; growth coefficient (K) was 0.62/year; growth performance (O) was 3.8; length at maturity (Lm) was 52.57cm; reproductive load (Lm/L8) was 0.52 and optimum length (Lopt) was 65.10cm. Likewise, natural, fishing and total mortalities were 0.93, 1.46 and 2.39 respectively. The values of exploitation rate (0.61) and ratio of total mortality and growth coefficient (3.85) showed that Mormyrus rume is most exploited in Ikere-gorge. Therefore, appropriate fishing regulations should be enforced to regulate fishing gears and mesh size that will fish Mormyrus rume at sustainable level. [ABSTRACT FROM AUTHOR]

Copyright of Knowledge & Management of Aquatic Ecosystems is the property of EDP Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Evolutionarily significant freshwater primitive fish, Chitala chitala (Hamilton-Buchanan, 1822) is an endangered featherback species with wide distribution in Indian subcontinent, Indonesia, Cambodia, Malaysia and Thailand. In this study, the complete mitochondrial genome is reported for the first time. The mitogenome of C. chitala was sequenced (16375 bp) and mapped to identify 13 protein coding genes (PCG), 22 transfer RNA genes, 2 rRNA genes (12S and 16SrRNA) and a control region. The ratio of synonymous and non synonymous substitutions (Ka/Ks) indicated that 10 genes evolved under purifying selection. Phylogenetic trees were constructed on the basis of concatenated 12 PCGs to ascertain its taxonomic relatedness with other seven orders along with osteoglossiformes. C. chitala displayed monophyly with other congeners, while Notopterus notopterus (Thailand) and Notopterus notopterus (India) showed marked distinction. [ABSTRACT FROM AUTHOR]

The fish heart ventricle has varied morphology and may have a specific morpho‐functional design in species adapted to extreme environmental conditions. In general, the Amazonian ichthyofauna undergoes constant variations in water temperature, pH and oxygen saturation, which makes these species useful for investigations of cardiac morphology. Arapaima gigas, a member of the ancient teleost group Osteoglossomorpha, is one of the largest freshwater fish in the world. This species has a specific heart metabolism that uses fat as the main fuel when O2 supplies are abundant but also can change to glycogen fermentation when O2 content is limiting. However, no information is available regarding its heart morphology. Here, we describe the heart of A. gigas, with emphasis on the ventricular anatomy and myoarchitecture. Specimens of A. gigas weighing between 0.3 and 4040 g were grouped into three developmental stages. The hearts were collected and the anatomy analyzed with a stereomicroscope, ultrastructure with a scanning electron microscope, and histology using toluidine blue, Masson's trichrome and Sirius red stains. The ventricle undergoes morphological changes throughout its development, from the initial saccular shape with a fully trabeculated myocardium and coronary vessel restricted to the subepicardium (Type I) (group 1) to a pyramidal shape with mixed myocardium and coronary vessels that penetrate only to the level of the compact layer (Type II) (groups 2 and 3). The trabeculated myocardium has a distinct net‐like organization in all the specimens, differing from that described for other teleosts. This arrangement delimits lacunae with a similar shape and distribution, which seems to allow a more uniform blood distribution through this myocardial layer. [ABSTRACT FROM AUTHOR]

In this transmission electron microscopy study, we describe the ultrastructure of the spermatozoon of Heterotis niloticus (Osteoglossiformes), which is distinguished by having two flagella. Our investigation also highlights the great diversity of sperm cell structures observed across osteoglossiform families, such as aflagellate (Gymnarchidae, Mormyridae), monoflagellate (Notopteridae, Pantodontidae) and biflagellate spermatozoa. As biflagellate spermatozoa are rare in vertebrates, we also summarize the orders and families known to possess this ultrastructural character, most of which are fishes. [ABSTRACT FROM AUTHOR]

Convergent evolution of a novel locomotor strategy implies that a fitness benefit may be associated with the new gait. Opportunities to study this phenomenon are often constrained by a lack of transitional taxa, but teleost fishes offer examples of extant species across such evolutionary shifts in gait. For instance, one species from Osteoglossiformes and the entire order of Gymnotiformes independently evolved a novel gait, gymnotiform locomotion, where thrust is produced by the undulation of an elongate anal fin. Here, we investigate whether this convergence in gait is also associated with similarities in shape, burst swimming abilities, and/or steady‐swimming energetics. Specifically, we measured body and fin morphology of fish within Gymnotiformes and Osteoglossiformes, along with closely related Siluriformes and Cypriniformes, to examine the link between gymnotiform locomotion and morphology in a phylogenetic context. Second, we tested the burst swimming capabilities and oxygen consumption during endurance swimming of a subset of the same gymnotiform, osteoglossiform, and cypriniform species, including "transitional" Osteoglossiformes that exhibit intermediate gaits, to determine whether the evolution of this specialized gait is associated with a change in either of these performance metrics. Our results suggest that convergence on the gymnotiform gait is associated with morphological convergence, but does not constrain a fish's maximum sprinting speeds or their energetic demands during steady swimming. [ABSTRACT FROM AUTHOR]

Abstract The Khanguet Aicha Barremian Biota site (KABBS) has yielded five actinopterygian taxa, four of are shortly described in this paper. The fish assemblage comprises the ichthyodectiform Cladocyclus sp., indeterminate osteoglossiform, chanoidei and stem otophysan, plus an ellimmichthyiform previously described. The fish assemblage recorded in the KABBS corresponds to a mixture of mostly freshwater taxa, the osteoglossiform, with taxa that dwell in both marine and freshwater environments (Cladocyclus and the chanoidei) and a marine fish (the stem otophysan). The association of the fish specimens with both freshwater conchostracan and marine shrimp indicates that the paleoenvironment was characterized by the influence of freshwater input. The fish assemblage contains a mixture of taxa that are found along the southern margin of the Tethys and along both margins of the incipient South Atlantic Ocean. Sedimentary facies of the Sidi Aïch Formation, which encompasses the KABBS include channel intraformational clasts, cross-bedded sandstones with mud drapes, herringbone cross-bedding; and sigmoidal cross-bedding suggesting strong tidal influences. Tidal facies together with paucity of bioturbation and mixed freshwater to marine fossils indicate that sedimentation took place mainly in restricted tidal flat ponds. The clayey varved facies, which dominates the KABBS corresponds to dark organic-rich and white organic-poor laminae interpreted as cyclic rhythmites reflecting neap-spring tidal cycles interrupted by flood events. Excellent preservation biota within KABBS and like-varved facies suggest deposition in low-energy restricted environments like mixed marine and fresh-water ponds along the tidal flats of the tidal meandering channel. Organic geochemistry analysis supported the idea of rapid burial associated with short-period sub-anoxic condition. [ABSTRACT FROM AUTHOR]

Diet composition and gut fullness of introduced clown featherback, Chitala ornata (Gray 1831) were assessed from three sampling sites (west, central, and east regions) of Laguna de Bay (Philippines). A total of 203 specimens (10.18-98.5 cm) were collected through the fish trap, seining and gillnet fishing from January to March 2014. Twelve stomachs were empty and excluded from the study. From the 191 stomachs, eleven prey items were identified, with Caridina sp. being the most important prey item by number (83.3 %) and frequency of occurrence (54.4 %). Teleosts prey, particularly an endemic Leiopotherapon plumbeus (Kner 1864) was the most important food item by volume (41.6 %). Index of Preponderance and Index of Relative Importance recognised Caridina sp., and L. plumbeus as the two most important food items (in order of magnitude). Gut fullness was significantly different among geographical sites (P < 0.01), with populations from the central region having the highest prey diversity and teleost prey consumption. An ontogenetic dietary shift was observed, where small-sized C. ornata (≤ 45 cm) consumed mainly on crustaceans, whilst teleosts were the main prey type for larger C. ornata (> 46 cm). The proportional weight of teleost-based diet and diversity of food items increased with C. ornata length. [ABSTRACT FROM AUTHOR]

Osteoglossiformes is one of the most ancient (Early Triassic) groups of freshwater teleosts and has at least one representative on each continent of the Southern Hemisphere, with the exception of Antarctica. Among its six described families, the Gymnarchidae occurs in many African rivers, including the river Nile, where Gymnarchus niloticus is its only representative. In this study we provide, for the first time, a comprehensive cytogenetic analysis for G. niloticus, which includes definition of the standard karyotype, C-banding, repetitive DNA mapping and comparative genomic hybridization, in order to investigate its chromosomal patterns and provide new data for comparative analyses with other Osteoglossiformes species. The 2 n was 34 (26 metacentric + 8 submetacentric) in both sexes, and C-positive heterochromatic bands were detected in the centromeric/pericentromeric regions of all chromosomes. The simultaneous detection of 18S and 5S ribosomal DNAs showed simple and non-syntenical locations for such sequences, and a Chromomycin A3-positive band was observed, which is co-localized within the 18S ribosomal RNA gene sequences. Fluorescence in situ hybridization using U2 small nuclear RNA, Rex 6 and some microssatelites as probes showed a scattered distribution among chromosomes. Data from comparative genomic hybridization experiments with some other African Osteoglossiformes species showed that all these species have an advanced stage of sequence divergence. The results highlight the evolutionary diversification of osteoglossiform fishes. [ABSTRACT FROM AUTHOR]

The molariform teeth of the mormyrid fish Hyperopisus bebe display a cone of orthodentine overlaid at their tip by a thick layer of enameloid (= acrodine). The teeth are fixed on a cellular bony tissue. This organization is classical for an actinopterygian and fits with the pattern classically observed in other osteoglossiform fishes. The presence of plicidentine and the hyoid tooth and tooth-plate morphology of this species may be related with crushing feeding habits. [ABSTRACT FROM AUTHOR]

The present study describes the morphology and histology of the digestive tract of juvenile pirarucu, which is a Neotropical fish species with great potential for aquaculture in the Amazon region. Three size classes of pirarucu juveniles from commercial fish farms were sampled for histological examination of the oesophagus, stomach, pyloric caeca, intestine and liver. The morphological and histological features of the pirarucu digestive tract are similar to other carnivorous teleosts and enable the species to ingest, store and digest large food items. Acidic and neutral mucins are secreted by the mucosa of the oesophagus, stomach, pyloric caeca and intestine to protect the mucosal epithelium and to lubricate and facilitate food passage along the digestive tract. Complex transverse folds are predominant in the intestinal mucosa and most likely contribute to optimization of the digestion and nutrient absorption processes, thereby offsetting the relatively short length of the intestine. The exocrine pancreas appears diffuse in the liver and mesentery around the pyloric region of the stomach, pyloric caeca and initial part of the intestine. The digestive tract morphology and thickness become increasingly developed with the size of pirarucu. [ABSTRACT FROM AUTHOR]

Species of the African electric fish in the genus Paramormyrops Taverne, Thys van den Audenaerde & Heymer, 1977 constitute a recently recognized species flock with an impressive diversity of electric signals, but only modest morphological differentiation. For more than a century, confusion has surrounded the identity of Paramormyrops sphekodes (Sauvage, 1879), the earliest described species in this genus. Here we compare the morphometrics of type material to new specimens collected at the type locality on the Ogooué River of Gabon from which we additionally study DNA sequences and electric organ discharges (EODs). Based on our findings, we revise the diagnosis and description of P. sphekodes and also identify and describe a new species of Paramormyrops that is large, common and widespread in the Ogooué River basin, but cryptic and easily confounded with P. sphekodes. We designate as lectotype of P. sphekodes a specimen formerly regarded, in error, as the holotype and a second specimen originally collected with the lectotype as paralectotype. We conclude that only nine additional specimens can be identified with confidence as P. sphekodes: four from the type locality and five from a second site 45 km away. Instead of being widespread as previously thought, P. sphekodes may be restricted to a small region of the upper Ogooué River basin. Additionally, we present a revised diagnosis for the genus Paramormyrops Taverne et al., 1977, and key to species from Lower Guinea. This study illustrates the value of vouchered EOD recordings and of revisiting type localities, and lays a foundation for additional systematic work on this group. [ABSTRACT FROM AUTHOR]

The clown knifefish is a facultative air breather, which is widely farmed in freshwater ponds in Vietnam. Here we report a very high nitrite tolerance (96 h LC 50 of 7.82 mM) in this species and examine the effects of 1 mM (LC 5 ) and 2.5 mM (LC 10 ) ambient nitrite on haemoglobin (Hb) derivatives, electrolyte levels, acid-base status, and total body water content during 7 days of exposure. Furthermore, we tested the hypothesis that erythrocyte methaemoglobin (metHb) reductase activity is upregulated by nitrite exposure. Plasma nitrite levels increased for 2–3 days but stayed below environmental levels and fell towards control values during the last half of the exposure period. Plasma nitrate, in contrast, rose continuously, reflecting detoxification of nitrite to nitrate. MetHb generated from the reaction between nitrite and erythrocyte Hb reached 38% at day 2, but then decreased to 17% by the end of experiment. The first order rate constant for metHb reduction by erythrocyte metHb reductase increased from 0.01 in controls to 0.046 min −1 after 6 days of nitrite exposure, showing up-regulation of this enzyme. While such upregulation has been suggested in nitrite-exposed fish species, this study provides the first experimental evidence. [ABSTRACT FROM AUTHOR]

Intensive sampling for vertebrate microfossils has yielded abundant fish remains in the Maastrichtian units of the Tremp Formation (southern Pyrenees, Catalonia, Spain). Samples were taken from eight new sites representing different palaeoenvironments including coastalwetlands and floodplains, in order to assess the fish diversity and to gain a better understanding of the last dinosaur-dominated ecosystems of northeastern Spain. The results suggest that a diverse ichthyofauna inhabited these transitional to inland fluvial settings throughout the Maastrichtian, comprising both marine and freshwater taxa. Three different chondrichthyans, eight basal neopterygians and at least seven teleostean species were found, the latter being more diverse than in other Maastrichtian localities in Europe. Fossil evidence from the studied late Maastrichtian assemblages suggests that teleosteans were present in all the trophic guilds. In addition, the oldest records for osteoglossids and perciforms in Europe, as well as for cypriniforms worldwide, are reported here. The findings from the southern Pyrenees also reveal ichthyofaunal turnover during the Late Cretaceous, with 'holosteans' being replaced by teleosteans. Moreover, Maastrichtian ichthyofaunas fromthe southern Pyrenees showAsian andNorth American biogeographical affinities. [ABSTRACT FROM AUTHOR]

The monophyletic order Osteoglossiformes represents one of the most ancestral groups of teleosts and has at least 1 representative in all continents of the southern hemisphere, with the exception of Antarctica. However, despite its phylogenetic and biogeographical importance, cytogenetic data in Osteoglossiformes are scarce. Here, karyotype and chromosomal characteristics of the lower Niger River population of the African butterfly fish Pantodon buchholzi, the sole species of the family Pantodontidae (Osteoglossiformes), were examined using conventional and molecular cytogenetic approaches. All specimens examined had 2n = 46 chromosomes, with a karyotype composed of 5 pairs of metacentric, 5 pairs of submetacentric, and 13 pairs of acrocentric chromosomes in both sexes. No morphologically differentiated sex chromosomes were identified. C-bands were located in the centromeric/pericentromeric region of all chromosomes and were associated with the single AgNOR site. FISH with ribosomal DNA probes revealed that both 5S and 18S rDNA were present in only 1 pair of chromosomes each, but did not colocalize. CMA 3 + bands were observed near the telomeres in several chromosome pairs and also at the 18S rDNA sites. The mapping of di- and trinucleotide repeat motifs, Rex6 transposable element, and U2 snRNA showed a scattered distribution over most of the chromosomes, but for some microsatellites and the U2 snRNA also a preferential accumulation at telomeric regions. This study presents the first detailed cytogenetic analysis in the African butterfly fish by both conventional and molecular cytogenetic protocols. This is the first of a series of further cytogenetic and cytogenomic studies on osteoglossiforms, aiming to comprehensively examine the chromosomal evolution in this phylogenetically important fish order. [ABSTRACT FROM AUTHOR]

Karyotyping is a basic method to investigate chromosomal evolution and genomic rearrangements. Sixteen genera within the basal teleost order Osteoglossiformes are currently described cytogenetically. Our study adds information to this chromosomal dataset by determining the karyotype of Campylomormyrus compressirostris , a genus of African weakly electric fish that has not been previously examined. Our results indicate a diploid chromosome number of 2n = 48 (4sm + 26m + 18a) with a fundamental number of FN = 72. This chromosome number is identical to the number documented for the sister taxon of the genus Campylomormyrus , i.e. , Gnathonemus petersii (2n = 48). These results support the close relationship of Campylomormyrus and Gnathonemus . However, the karyotype formula of C. compressirostris is different from Gnathonemus petersii , thereby confirming the high variability of karyotype formulae within the Mormyridae. We infer that the differences in chromosome number and formula of Campylomormyrus relative to other mormyrids may be caused by Robertsonian fusion and pericentric inversion. In addition to the karyotype description and classification of Campylomormyrus , a ChromEvol analysis was used to determine the ancestral haploid chromosome number of osteoglossiform taxa. Our results indicate a relatively conservative haploid chromosome number of n = 24 for the most recent common ancestor of Osteoglossiformes and for most of the internal nodes of osteoglossiform phylogeny. Hence, we presume that the high chromosome variability evolved recently on multiple independent occasions. Furthermore, we suggest that the most likely ancestral chromosome number of Mormyridae is either n = 24 or n = 25. To the best of our knowledge this is the first attempt to determine and classify the karyotype of the weakly electric fish genus Campylomormyrus and to analyze chromosomal evolution within the Osteoglossiformes based on Maximum Likelihood and Bayesian Inference analyses. [ABSTRACT FROM AUTHOR]

African weakly-electric fishes (Mormyridae) are able to communicate through species-specific electric signals; this feature might have favoured the evolutionary radiation observed in this family (over 200 species) by acting as an effective pre-zygotic isolation mechanism. In the present study we used mitochondrial ( cytb ) and nuclear ( rps7 , scn4aa ) markers in order to reconstruct a species-phylogeny and identify species boundaries for the genus Campylomormyrus , by applying inference methods based on the multispecies coalescent model. Additionally, we employed 16 microsatellite markers, landmark-based morphometric measurements, and electro-physiological analyses as independent lines of evidence to the results obtained from the sequence data. The results show that groups that are morphologically different are also significantly divergent at the genetic level, whereas morphologically similar groups, displaying dissimilar electric signals, do not show enough genetic diversity to be considered separate species. Furthermore, the data confirm the presence of a yet undescribed species within the genus Campylomormyrus . [ABSTRACT FROM AUTHOR]