Cytogenetics Meets Genomics: Cytotaxonomy and Genomic Relationships among Color Variants of the Asian Arowana Scleropages formosus.

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.

A biflagellate spermatozoon in the African bonytongue Heterotis niloticus (Teleostei, Osteoglossidae).

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.

Genetic differentiation of a primitive teleost, the African bonytongue Heterotis niloticus, among river basins and within a floodplain river system in Benin, West Africa.

Examination of eight microsatellite DNA loci revealed high levels of genetic differentiation among populations of the African bonytongue Heterotis niloticus from three river basins that constitute important fishing areas in Benin. Low levels of population genetic differentiation were detected within the Ouemé-Sô River floodplain system. These results have important implications for conservation and management of stocks supporting important inland fisheries in West Africa.

From Chromosomes to Genome: Insights into the Evolutionary Relationships and Biogeography of Old World Knifefishes (Notopteridae; Osteoglossiformes).

In addition to its wide geographical distribution, osteoglossiform fishes represent one of the most ancient freshwater teleost lineages; making it an important group for systematic and evolutionary studies. These fishes had a Gondwanan origin and their past distribution may have contributed to the diversity present in this group. However, cytogenetic and genomic data are still scarce, making it difficult to track evolutionary trajectories within this order. In addition, their wide distribution, with groups endemic to different continents, hinders an integrative study that allows a globalized view of its evolutionary process. Here, we performed a detailed chromosomal analysis in Notopteridae fishes, using conventional and advanced molecular cytogenetic methods. Moreover, the genetic distances of examined species were assessed by genotyping using diversity arrays technology sequencing (DArTseq). These data provided a clear picture of the genetic diversity between African and Asian Notopteridae species, and were highly consistent with the chromosomal, geographical, and historical data, enlightening their evolutionary diversification. Here, we discuss the impact of continental drift and split of Pangea on their recent diversity, as well as the contribution to biogeographical models that explain their distribution, highlighting the role of the Indian subcontinent in the evolutionary process within the family.

Extreme nitrite tolerance in the clown knifefish Chitala ornata is linked to up-regulation of methaemoglobin reductase activity.

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 (96h LC50 of 7.82mM) in this species and examine the effects of 1mM (LC5) and 2.5mM (LC10) ambient nitrite on haemoglobin (Hb) derivatives, electrolyte levels, acid-base status, and total body water content during 7days of exposure. Furthermore, we tested the hypothesis that erythrocyte methaemoglobin (metHb) reductase activity is upregulated by nitrite exposure. Plasma nitrite levels increased for 2-3days 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 0.046min-1 after 6days 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.

Karyotype description of the African weakly electric fish Campylomormyrus compressirostris in the context of chromosome evolution in Osteoglossiformes.

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.

Olfactory Sensory Neuron Morphotypes in the Featherback Fish, Notopterus notopterus (Osteoglossiformes: Notopteridae).

BACKGROUND: As in other vertebrates, olfactory sensory neurons (OSNs) in fishes are the main components of sensory part of olfactory epithelium that relay olfactory information (smell and taste) to the brain. PURPOSE: Objective of the present study was to analyze if any polymorphism occurs in the OSNs in a featherback fish, Notopterus notopterus as far as the teleost lineage is concerned. METHODS: With the help of neuronal staining technique, polymorphism of OSNs in N. notopterus was studied. RESULTS: Three polymorphic forms of OSNs were identified which are ciliated OSNs, microvillus OSNs and crypt OSNs. These morphotypes were identified on the basis of location of their somata within the depth of olfactory epithelium and resulting length of their dendrites. The ciliated OSNs have basally situated somata and long, thin dendrites with a few apically arranged cilia while microvillous OSNs have somata located midway in the epithelium and thick moderate-length dendrites with microvilli. Third cell type is crypt OSNs which are spherical or pear-shaped, located apically just close to the epithelial surface having cilia and microvilli in an invagination and devoid of any dendrite. CONCLUSION: N. notopterus belongs to order Osteoglossiformes which is a representative of an early evolutionary lineage of teleost fishes. OSN polymorphism reported in the present work indicates that it is a fairly conserved trait throughout the evolution of teleosts. To our knowledge, we are the first ones to report OSN polymorphism in a member of the order Osteoglossiformes.

The first transcriptome and genetic linkage map for Asian arowana.

Asian arowana or dragonfish (Scleropages formosus) is an important fish species due to its unusual breeding biology and high economic value in the ornamental fish markets. In the present study, we aimed to (i) create the first transcriptome by Roche 454 pyrosequencing of Asian arowana brain and gonad samples; (ii) identify differentially expressed genes between the two sexes and develop microsatellite (SSR) markers; and (iii) construct a first-generation SSR-based genetic linkage map. A total of over 1.3 million reads were obtained from the brain and gonad of adult Asian arowana individuals through pyrosequencing. These reads were assembled into 16,242 contigs that were further grouped into 13,639 isogroups. BLASTX annotation identified a total of 8316 unique proteins from this data set. Many genes with sexually dimorphic expression levels and some putatively involved in sex development were identified. A total of 316 EST-SSRs and 356 new genomic-SSRs were developed by screening through the current transcriptome data set and SSR-enriched genomic libraries. The first genetic linkage map of the species was constructed based on these markers. Linkage analysis allowed for mapping of 308 markers to 28 linkage groups (LGs), ranging in size from 14.9 to 160.6 cM. The potentially sex-associated gene sox9 was mapped to LG4 on the consensus linkage map. Pairwise putative conserved syntenies between the Asian arowana, zebrafish, and three-spined stickleback were also established. These resources will help the conservation of the species through better understanding of its phylogenetics, genomics and biology, and comparative genome analysis within the Osteoglossidae family.

Feeding frequency affects feed intake and growth in juvenile pirarucu (Arapaima gigas)

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. (AU)

Morphology and histology of the pirarucu (Arapaima gigas) digestive tract / Morfología e histología del tubo digestivo del paiche (Arapaima gigas)

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.

El presente trabajo describe la morfología e histología del tracto digestivo de una especie juvenil de paiche, un pez neotropical con gran potencial acuícola en la region Amazónica. Se tomaron muestras de tres clases de tamaño de juveniles de paiche de granjas acuícolas comerciales para examen histológico del esófago, estómago, ciego pilórico, intestino e hígado. El tracto digestivo del paiche tiene características morfológicas e histológicas comunes a otros teleósteos carnívoros que permiten a la especie la ingestión, el almacenamiento y la digestión de grandes alimentos. Mucinas ácidas y neutras son secretadas por la capa mucosa del esófago, estómago, ciego pilórico e intestino para proteger el epitelio de esta capa, además de lubricar y facilitar el paso de los alimentos a lo largo del tracto. Pliegues complejos y de orientación transversal son predominantes en la mucosa intestinal, contribuyendo, probablemente, a la optimización de los procesos de digestión y absorción de nutrientes, y compensando la longitud relativamente corta del intestino. El páncreas exócrino se encuentra difuso dentro del hígado y en el mesenterio alrededor de la región pilórica del estómago, ciego pilórico y porción inicial del intestino. La morfología y el espesor del tubo digestorio se desarrollan de forma gradual a medida que el paiche crece.

Anatomical Behavior of the Celiacomesenteric Artery of Pirarucu Arapaima gigas Cuvier, 1817 (Osteoglossiforme, Arapaimidae) / Comportamiento Anatómico de la Arteria Celiacomesentérica en Pirarucu Arapaima gigas Cuvier, 1817 (Osteoglosiforme, Arapaimidae)

The pirarucu, Arapaimidae family fish, is one of the most important and emblematic species of Amazon. To investigate their circulatory system anatomies features were used 10 specimens with 74 cm medium total length, from river Araguaia lakes, Sao Miguel do Araguaia, Goias, Brazil. The fishes had their celomatic cavity open with dorsal aorta artery identified and cannulation where was injected synthetic latex. Fixation of those specimens was by injection of 10% formalin. In that specie, the coeliac-mesenteric artery is the only one arterial vessel responsible to digestive tract flow and always ramified from 2nd, 3rd and 4th left efferent branchial arteries. The stomach is flowing by coeliac artery and a gastric branch of the cecal ventral artery; intestine receives coeliac-mesenteric artery branchs and cranial and caudal mesenteries arteries branchs; the dorsal and ventral cecum are supplied by cecal dorsal and ventral arteries respectively.

El pirarucu, pez de la familia Arapaimidae, es una de las especies más importantes y emblemáticas de la ictiofauna amazónica. Para estudiar las características anatómicas de su sistema circulatorio, fueron utilizados 10 ejemplares de Arapaima gigas, con un longitud total media de 74 cm, provenientes de lagos del río Araguaia, Sao Miguel do Araguaia, Goiás, Brasil. A los peces se les abrió la cavidad celomática donde se identificó y canalizó la arteria aorta dorsal, injectándose una solución coloreada de látex sintético. La fijación del material se realizó con inyecciones de formol al 10%. La arteria celiacomesentérica es responsable de la irrigación del tubo digestivo y tiene origen en las 2ª, 3ª y 4ª arterias branquiales eferentes izquierdas. El estómago está irrigado por la arteria celíaca y por una rama gástrica de la arteria cecal ventral. El intestino recibe ramas arteriales procedentes de la arteria celiacomesentérica y de las arterias mesentéricas craneal y caudal; los ciegos dorsal y ventral están irrigados por las arterias cecales dorsal y ventral, respectivamente.