The emerging vertebrate model species for neurophysiological studies is Danionella cerebrum, new species (Teleostei: Cyprinidae)

The four described species of Danionella are tiny, transparent fishes that mature at sizes between 10–15 mm, and represent some of the most extreme cases of vertebrate progenesis known to date. The miniature adult size and larval appearance of Danionella, combined with a diverse behavioral repertoire linked to sound production by males, have established Danionella as an important model for neurophysiological studies. The external similarity between the different species of Danionella has offered an important challenge to taxonomic identification using traditional external characters, leading to confusion over the identity of the model species. Using combined morphological and molecular taxonomic approaches, we show here that the most extensively studied species of Danionella is not D. translucida, but represents an undescribed species, D. cerebrum n. sp. that is externally almost identical to D. translucida, but differs trenchantly in several internal characters. Molecular analyses confirm the distinctiveness of D. cerebrum and D. translucida and suggest that the two species are not even sister taxa. Analysis of the evolution of sexual dimorphisms associated with the Weberian apparatus reveals significant increases in complexity from the simpler condition found in D. dracula, to most complex conditions in D. cerebrum, D. mirifica and D. translucida.

The broad role of Nkx3.2 in the development of the zebrafish axial skeleton

The transcription factor Nkx3.2 (Bapx1) is an important chondrocyte maturation inhibitor. Previous Nkx3.2 knockdown and overexpression studies in non-mammalian gnathostomes have focused on its role in primary jaw joint development, while the function of this gene in broader skeletal development is not fully described. We generated a mutant allele of nkx3.2 in zebrafish with CRISPR/Cas9 and applied a range of techniques to characterize skeletal phenotypes at developmental stages from larva to adult, revealing loss of the jaw joint, fusions in bones of the occiput, morphological changes in the Weberian apparatus, and the loss or deformation of bony elements derived from basiventral cartilages of the vertebrae. Axial phenotypes are reminiscent of Nkx3.2 knockout in mammals, suggesting that the function of this gene in axial skeletal development is ancestral to osteichthyans. Our results highlight the broad role of nkx3.2 in zebrafish skeletal development and its context-specific functions in different skeletal elements.

Abnormal craniofacial and spinal bone development with col2a1a depletion in a zebrafish model of CHARGE syndrome

CHARGE syndrome patients commonly display craniofacial abnormalities. Furthermore, most patients show features of idiopathic scoliosis, reduced bone mineral density and in a few cases osteopenia. While several clinical cases and studies have documented the skeletal deformities in CHARGE syndrome bearing CHD7 mutations, the underlying mechanisms of the disorder remain elusive. Here, we detect and quantitatively analyze skeletal abnormalities in larval and adult chd7-/- zebrafish.We show that young chd7-/- larvae present with abnormal craniofacial development, especially related to cartilage. We also observe scoliosis-like spinal deformations at 9 dpf. Gene expression analysis confirmed the reduction of osteoblast markers and Pparγ targets. MicroCT analyses identified abnormal craniofacial structures, Weberian apparatus and vertebral body morphology in chd7-/- mutants, with highly mineralized inclusions, along with significant variances in bone mineral density and bone volume. Notably, we detect a specific depletion of Col2a1a in the cartilage of craniofacial regions and vertebrae, in line with a significantly reduced number of chondrocytes.Our study is the first to elucidate the mechanisms underlying morphological changes in craniofacial structure and vertebrae of adult chd7-/- zebrafish. The chd7-/- mutant zebrafish will be beneficial in future investigations of the underlying pathways of both craniofacial and spinal deformities commonly seen in CHARGE syndrome.

A new species of Pseudobunocephalus Friel, 2008 (Siluriformes: Aspredinidae) from the lower Tocantins and Mearim river drainages, North and Northeast of Brazil

Pseudobunocephalus timbira, new species, is described from streams of the lower Tocantins and the Mearim river drainages, in North and Northeast of Brazil. Pseudobunocephalus timbira can be distinguished from all congeners by having the second hypobranchial and the third basibranchial cartilaginous (vs. ossified). Additionally, it can be dintinguished from P. lundbergi by the following putative apomorphic features within Pseudobunocephalus: posterolateral process of premaxilla present (vs. absent); bony knobs in dorsal lamina of Weberian apparatus absent (vs. present); distal end of posterior margin of 5th parapophysis not enlarged (vs. enlarged); number of ribs three (vs. four or five) and infraorbital sensory canal entering neurocranium via frontal (vs. via sphenotic). It is distinguished from P. bifidus and P. iheringii by having a gracile body not surpassing 34 mm SL (vs. robust body, reaching up to 59 mm SL, respectively); by having the posterior margin of cranial fontanel concave (vs. posterior margin somewhat straight with parieto-supraoccipital extending anteriorly); by having a conspicuous knobby ornamentation on dorsal surface of skull (vs. skull knobs slightly pronounced); by having Weberian ventral blade of hemal canal opened (vs. closed) and by the absence of serrations on the proximal portion of the anterior margin of pectoral-fin spine (vs. serrations covering entire anterior margin of the pectoral spine). Additionally, it can be distinguished from P. amazonicus, P. rugosus and P. quadriradiatus, by having the posterolateral mental barbel with at least one fleshy lobe located proximally along the posterior margin (vs. posterolateral mental barbel simple, not having fleshy lobes). It also differs from P. amazonicus and P. rugosus by having five branchiostegal rays (vs. four). It also can be distinguished from P. amazonicus by having the contact of hyomandibula cartilage with neurocranium limited to the sphenotic (vs. extending to both sphenotic and pterotic); by having the ventral blade of Weberian apparatus open (vs. closed) and by anterior exit of hemal canal in abdominal vertebra (vs. in complex vertebra); from P. rugosus by coloration of proximal portion of caudal fin similar to rest of caudal fin (vs. clear patch) and from P. quadriradiatus by the total number of pectoral fin-rays six (vs. five). Variable characteristics within Pseudobunocephalus species are summarized and comments on the phylogenetic relationships and the disjunct distribution of the new species are made. [Species zoobank url: urn:lsid:zoobank.org:act:392F95E0-86E1-4386-8779-C4F71098DBCC]

Morfologi tulang belakang (ossa vertebrae) ikan keureling, Tor tambroides (Bleeker, 1854)

This study aims to describe the axial skeleton morphology (ossa vertebrae) of Thai mahseer’s,Tor tambroides (Bleeker 1854). A 5 kg of 65 cm fish sample were obtained from fish trader in the Tangse River area of Pidie district.. The axial skeleton preparations processed at the Laboratory of Mathematics and Natural Sciences, Al Muslim University, Bireuen district. The identification of terminology was done at Integrated Biology Laboratory, Biology Department, Faculty of Science and Technology, Ar-Raniry Islamic State University. The keureling’s axial skeleton processed by physically and chemically.. Axial skeleton was arranged into a single piece to analyze every part of it. Every part of axial skeleton documented by using Canon EOS 700D camera and processed by Adobe Photoshop CS3. The labeling of each part of the axial skeleton was done by comparing the similarity of the shape and location of each part of the fish axial skeleton that has been studied previously, either from the same family or from the different family.The results showed that Keureling had four axial vertebrae bones belonging to the weberian apparatus, 19 ossa abdominal vertebrae, 18 pairs ossa costales, 16 ossa caudal vertebrae and one os urostyles vertebrae.AbstrakPenelitian ini bertujuan untuk mendeskripsikan morfologi tulang belakang (ossa vertebrae) ikan keureling, Tor tam-broides (Bleeker, 1854). Contoh ikan diperoleh dari pedagang ikan di wilayah sungai Tangse Kabupaten Pidie dengan bobot 5 kg dan panjang 65 cm. Tahapan pembuatan preparat tulang belakang dilakukan di Laboratorium Matematika dan Ilmu Pengetahuan Alam, Universitas Al Muslim Kabupaten Bireuen. Identifikasi terminologi tulang belakang ikan dilakukan di Laboratorium Terpadu Biologi, Program studi Biologi, Fakultas Sains dan Teknologi, Universitas Islam Negeri Ar-Raniry. Pembuatan preparat tulang belakang dilakukan secara fisik dan kimiawi. Tulang belakang yang telah bersih dirangkai menjadi satu kesatuan untuk dianalisis setiap bagian-bagiannya. Pemotretan setiap bagian tulang bela-kang dilakukan dengan menggunakan kamera Canon EOS 700D dan diolah dengan menggunakan Adobe Photoshop CS3. Penamaan setiap bagian tulang belakang dilakukan dengan cara membandingkan kemiripan bentuk dan letak dari setiap bagian tulang belakang ikan yang telah diteliti sebelumnya, baik dari famili yang sama maupun dari famili yang berbeda. Hasil penelitian menunjukkan ikan keureling memiliki empat buah tulang axial vertebrae yang termasuk da-lam tulang Weber (Weberian apparatus), 19 ossa abdminal vertebrae, 18 pasang ossa costae, 16 ossa caudal vertebrae dan satu os urostyles vertebrae.