An ancient truncated duplication of the anti-Mullerian hormone receptor type 2 gene is a potential conserved master sex determinant in the Pangasiidae catfish family

The evolution of sex determination (SD) mechanisms in teleost fishes is amazingly dynamic, as reflected by the variety of different master sex-determining genes identified, even sometimes among closely related species. Pangasiids are a group of economically important catfishes in many South-Asian countries, but little is known about their sex determination system. Here, we generated novel genomic resources for 12 Pangasiid species and provided a first characterization of their SD system. Based on an Oxford Nanopore long-read chromosome-scale high quality genome assembly of the striped catfish Pangasianodon hypophthalmus, we identified a duplication of the anti-Mullerian hormone receptor type II gene (amhr2), which was further characterized as being sex-linked in males and expressed only in testicular samples. These first results point to a male-specific duplication on the Y chromosome (amhr2by) of the autosomal amhr2a. Sequence annotation revealed that the P. hypophthalmus Amhr2by is truncated in its N-terminal domain, lacking the cysteine-rich extracellular part of the receptor that is crucial for ligand binding, suggesting a potential route for its neofunctionalization. Short-read genome sequencing and reference-guided assembly of 11 additional Pangasiid species, along with sex-linkage studies, revealed that this truncated amhr2by duplication is also conserved as a male-specific gene in many Pangasiids. Reconstructions of the amhr2 phylogeny suggested that amhr2by arose from an ancient duplication / insertion event at the root of the Siluroidei radiation that is dated around 100 million years ago. Altogether these results bring multiple lines of evidence supporting that amhr2by is an ancient and conserved master sex-determining gene in Pangasiid catfishes, a finding that highlights the recurrent usage of the transforming growth factor β pathway in teleost sex determination and brings another empirical case towards the understanding of the dynamics or stability of sex determination systems.

Genetic Variation Analysis between Wild and Cultured Pangasianodon hypopthalmus Using COI and Cytochrome b Among Asian Countries

One of the top species in the aquaculture sector, known as striped catfish or Pangasianodon hypophthalmus, is an important and valuable freshwater fish in many countries. Due to the high demand for this species, their number has declined to "threatened" levels. Hence, the purpose of this study is to analyse the genetic variation of wild and cultured striped catfish collected from five producers in Asian countries; Thailand, Vietnam, Indonesia, India, and Philippines, by using mitochondrial DNA partial region data sequence; CO1 and cytochrome b gene. Population analyses using 395 base pairs length for CO1 and 275 base pairs length of cytochrome b partial region nucleotide sequence have shown no significance difference between wild and cultured striped catfish. Vietnam species had shown a wide range of genetic distance of the intrapopulation compared with other countries in the range of 0.000-0.040 for CO1 gene and 0.003-0.008 for cytochrome b gene. The Neighbour-joining method has also been used to construct phylogenetic trees using CO1 gene; the tree formed few subclades with mixed populations, and the tree using cytochrome b showed only Vietnam species divided into a few sub-populations. For the other four countries, Thailand, Indonesia, India, and Philippines were in the same group. Hence, this study's findings may provide a reference for inter and intra-relationships of P. hypophthalmus that may help in the aquaculture activity of this striped catfish.

El pez basa, panga o pangasius, Pangasianodon hypophthalmus (Sauvage, 1878) (Siluriformes: Pangasiidae) en Colombia

En el 2011 se realizó un análisis de la especie Pangasionodon hypophthalmus, que formó parte de la publicación sobre las especies acuáticas exóticas (Gutiérrez et al., 2012) y de conceptos posteriores como respuesta a requerimientos por parte del Minambiente, la Fiscalía General de la Nación y la Autoridad Nacional de Licencias Ambientales (Anla), que consideró los resultados de dicha evaluación como uno de los elementos de análisis para la posterior negación de la solicitud de introducción y cría del pez basa en el departamento del Huila, realizada por la organización Acuapez (Resolución 0389 de 2013). En 2016, tras la comprobación de la presencia de la especie en el país como resultado de su introducción ilegal (Valderrama et al., 2016), se reabrió la discusión sobre la introducción de la especie de manera legal, lo que convocó al Instituto Humboldt, como apoyo técnico del Minambiente, a contribuir con la generación de información técnica y científica para la toma de decisiones informada por parte de las autoridades de los sectores ambiental, agricultura y comercio. En el marco de este compromiso, el Instituto Humboldt priorizó la coordinación con redes de expertos nacionales, así como ejercicios internos interdisciplinarios con la perspectiva de aportar información sobre el estatus de la especie en el país, su distribución y las posibles interacciones con especies nativas en ecosistemas naturales. Con el propósito de alcanzar estos objetivos se identificó la necesidad de contar con toda la información bibliográfica necesaria y realizar los modelamientos sobre distribución, presencia actual y potencial en el país con la información disponible hasta el momento.

Influences of Salinity on Embryonic and Larval Development of Striped Catfish Pangasianodon hypophthalmus

Salinity intrusion in coastal areas due to climate change is alarming. In this study, the effects of salinity on embryonic and larval development of striped catfish (Pangasianodon hypophthalmus) were studied experimentally. Embryos and larvae were exposed to seven salinity treatments (0, 2, 4, 6, 8, 10, and 12 ppt), each with three replications. Considerable survivability of embryos was recorded up to 6 ppt salinity. Mortality of embryos significantly increased at 8 and 10 ppt salinity, and 100% mortality was displayed within 12 h of exposure at 12 ppt salinity. The rate of hatching was significantly reduced at 8 and 10 ppt salinity. The 24 h lethal concentration (LC50) value of salinity for embryo was 11.24 ppt. Different types of deformities, such as undeveloped yolk sac, elongated gastrula yolk sac, and yolk sac bud, were highest at 10 ppt salinity. Similar to the embryo, considerable survivability of larvae was recorded up to 6 ppt salinity, and 100% mortalities were found within 24 h of exposure at 12 ppt salinity. The 24 and 48 h LC50 values of salinity for larvae were 10.63 and 8.48 ppt, respectively. Several types of deformities, including yolk sac ulceration, spine scoliosis, tail bent, yolk sac edema, and compromised swim bladder inflation, were highest at 10 ppt salinity after 48 h of exposure. Within 24 h of exposure, about 80% yolk sac of the larvae was absorbed at 8 and 10 ppt salinity, while 30%–50% yolk sac was absorbed at 0–6 ppt salinity. Growth rates in terms of length and weight were higher at 0, 2, and 4 ppt salinity and moderate at 6 and 8 ppt salinity. Overall, the current findings define the limits to optimize hatchery procedures for the culture of this species in low saline brackish water.