A study on the seasonal cyclicity of ovarian development in adult Himalayan snow trout, Schizothorax plagiostomus.

Schizothorax plagiostomus, commonly known as snow trout, is a popular food fish found in parts of Central Asia and the Indo-Himalayan region. Despite such a broad range of distribution and potential financial value, it is a highly neglected cold-water ichthyofauna. Furthermore, an alarming decline in Schizothoracine population has been reported in the recent past due to climate change and uncontrolled anthropogenic interference. In this study, the seasonal variations in ovarian architecture and development were examined in adult S. plagiostomus from Garhwal Himalayan region, Uttarakhand, India. Ovarian-somatic index ranged from 16.86 ± 0.29 to 0.31 ± 0.56, with a maximal value in September and a minimal value in April. Ovarian histology revealed the abundance of primary growth oocytes in resting and preparatory stages; primary/secondary vitellogenic oocytes with numerous cortical alveoli were predominant in the developing stage of pre-spawning ovaries; secondary/tertiary vitellogenic oocytes were conspicuous in actively spawning ovaries; and atretic follicles/oocytes were discernible during the regressing stage of spent ovaries. Scanning electron microscopy of mature ova (mean diameter 2.003 ± 0.01 mm) prominently showed the structure micropyle (mean diameter 12.93 ± 3.38 µm). Fecundity analyses suggested that September was the principal breeding season, whereas residual spawning occurred with fresh rain in late winter during February-March. Collectively, this is the first comprehensive qualitative and quantitative report of the seasonal variations in the ovarian development and function for S. plagiostomus. These data may provide valuable information towards the captive breeding programme as well as conservation and management for Schizothoracine fishes in normal and altered climatic conditions.

Resolving the phylogenetic relationship of Himalayan snow trout Schizothorax plagiostomus with other species of Schizothoracine using mitochondrial CO-I and Cyt b genes.

BACKGROUND: The classification of the sub-family Schizothoracinae has been debatable due to the overlap in morphological characters. There are discrepancies between classical taxonomy and molecular taxonomy, as well. In the present study, mitochondrial genes CO-I and Cyt b were sequenced to elucidate the phylogenetic status of three species of the genus Schizothorax. METHODS AND RESULTS: In total, 29 samples of three species viz., S. plagiostomus, S. progastus, and S. richardsonii, were collected from rivers of Uttarakhand, India. For phylogenetic analyses, 40 sequences of CO-I and 41 sequences of Cyt b of Schizothoracinae species were downloaded from NCBI. The highest genetic divergence based on CO-I (16.08%) is between S. plagiostomus and Ptychobarbus dipogon, while the lowest divergence (0.00%) is between 10 pairs of species. The highest divergence based on Cyt b (19.43%), is between S. niger and Gymnocypris eckloni, while the lowest divergence (0.00%) is between four pairs of species. The divergence (0.00% for CO-I and 2.38% for Cyt b) between S. chongi and S. kozlovi, seems a case of convergent molecular evolution of the CO-I gene and in this case, CO-I alone cannot be used to differentiate these two species. CONCLUSION: The simultaneous use of two molecular markers along with morphomeristic data is a better strategy for the classification of the sub-family Schizothoracinae. These results will be a resource dataset for determining the taxonomical status of Schizothoracine species and will help in the conservation and commercial production of these commercially important fish species.

Recent Update on Retinoic Acid-Driven Initiation of Spermatogonial Differentiation.

Germ cells (Gc) propagate the genetic information to subsequent generations. Diploid (2n) Gc get transformed to specialized haploid (n) gametes by mitotic and meiotic divisions in adult gonads. Retinoic acid (RA), an active derivative of vitamin A (retinol), plays a critical role in organ morphogenesis and regulates the meiotic onset in developing Gc. Unlike ovaries, fetal testes express an RA-degrading enzyme CYP26B1, and thereby, male Gc fail to enter into meiosis and instead get arrested at G0/G1 stage, termed as gonocytes/pro-spermatogonia by embryonic (E) 13.5 days. These gonocytes are transformed into spermatogonial stem/progenitor cells after birth (1-3 days of neonatal age). During post-natal testicular maturation, the differentiating spermatogonia enter into the meiotic prophase under the influence RA, independent of gonadotropic (both FSH and LH) support. The first pulse of RA ensures the transition of undifferentiated type A spermatogonia to differentiated A1 spermatogonia and upregulates STRA8 expression in Gc. Whereas, the second pulse of RA induces the meiotic prophase by augmenting MEIOSIN expression in differentiated spermatogonia B. This opinion article briefly reviews our current understanding on the RA-driven spermatogonial differentiation in murine testes.