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.

Feeding frequency affects feed intake and growth in juvenile pirarucu (Arapaima gigas) / Frequência alimentar afeta a ingestão alimentar e o crescimento de juvenis de 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)

O pirarucu é uma das principais espécies de peixe para o desenvolvimento da aquicultura na região amazônica. Neste trabalho foi avaliada a frequência de alimentação ideal para juvenis de pirarucu com base em crescimento e eficiência alimentar. Juvenis de aproximadamente 80 g foram alimentados uma, duas, três ou quatro vezes ao dia até a saciedade aparente durante 63 dias. Maior crescimento, ingestão alimentar e gordura corporal foram observados nos peixes alimentados três ou quatro vezes ao dia em comparação com aqueles alimentados uma ou duas vezes ao dia. Não houve diferença significativa para as taxas de conversão alimentar, retenção proteica e retenção energética entre os tratamentos, indicando que o aumento da frequência de alimentação não resultou em prejuízo da eficiência de utilização do alimento. O consumo médio de alimento por refeição foi maior nos peixes alimentados apenas uma vez ao dia, que provavelmente desenvolveram comportamento hiperfágico. Os resultados sugerem que três refeições diárias foram suficientes para garantir o consumo de alimento e crescimento adequados nessa fase.(AU)

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)

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.

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.

Feeding of juvenile pirarucu (Arapaima gigas, Arapaimidae) in their natural environment, lago Quatro Bocas, Araguaiana-MT, Brazil

The stomach content of samples of juvenile Arapaima gigas was analized to obtain information about feeding in natural environments. This species occurs in the Amazonian basin, predominantly in floodplain environment. This is the case of the valley of the middle rio Araguaia, where the lago Quatro Bocas is situated. Juveniles A. gigas prefered insects, microcrustaceans and gastropods, most of autochthonous origin. All the stomachs examined contained at least one food item.

Analisou-se no presente estudo, o conteúdo estomacal de juvenis de Arapaima gigas com a finalidade de se ampliar informações sobre sua alimentação em ambiente natural. Esta espécie ocorre na bacia Amazônica, com predominância em ambientes de planície. Este é o caso do vale do médio rio Araguaia, onde se situa o lago Quatro Bocas. Juvenis de A. gigas apresentaram preferência por insetos, microcrustáceos e gastrópodes, sendo sua maioria de origem autóctone. Todos os estômagos examinados continham pelo menos um item alimentar.

Feeding of juvenile pirarucu (Arapaima gigas, Arapaimidae) in their natural environment, lago Quatro Bocas, Araguaiana-MT, Brazil

The stomach content of samples of juvenile Arapaima gigas was analized to obtain information about feeding in natural environments. This species occurs in the Amazonian basin, predominantly in floodplain environment. This is the case of the valley of the middle rio Araguaia, where the lago Quatro Bocas is situated. Juveniles A. gigas prefered insects, microcrustaceans and gastropods, most of autochthonous origin. All the stomachs examined contained at least one food item.

Analisou-se no presente estudo, o conteúdo estomacal de juvenis de Arapaima gigas com a finalidade de se ampliar informações sobre sua alimentação em ambiente natural. Esta espécie ocorre na bacia Amazônica, com predominância em ambientes de planície. Este é o caso do vale do médio rio Araguaia, onde se situa o lago Quatro Bocas. Juvenis de A. gigas apresentaram preferência por insetos, microcrustáceos e gastrópodes, sendo sua maioria de origem autóctone. Todos os estômagos examinados continham pelo menos um item alimentar.