We sequenced and assembled three whole mitogenome sequences of the commercially important snakeskin gourami Trichopodus pectoralis isolated from Malaysia (introduced), Viet Nam (native) and Thailand (native). The mitogenome length range from 16,397 to 16,420 bp. The final partitioned nucleotide alignment consists of 14,002 bp and supports the monophyly of the genus Trichopodus (95% ultrafast bootstrap support) with T. trichopterus forming a sister group with the members of T. pectoralis.
Eighty-four specimens collected from 13 populations from Malaysia, Thailand, and Vietnam were analysed, revealing 21 putative haplotypes with overall estimated haplotype and nucleotide diversities of 0.79 and 0.0079, respectively. High levels of diversity and an absence of founder effects were observed among populations in peninsular Malaysia. In contrast, populations from Sarawak exhibited low genetic diversity, which is a typical sign of colonies introduced from a single source. Historical translocation of Trichopodus pectoralis from Thailand to Malaysia, as well as to the Philippines, Indonesia, and Myanmar was apparent. Historical introduction of T. pectoralis from Vietnam was also detected in peninsular Malaysia.
To obtain well spread chromosomes, the cytogenetic protocol for Pangasianodon hypophthalmus and Clarias gariepinus were optimized. This includes, the colchicine concentration (0.01%, 0.025%, 0.05%)/exposure duration (1, 3, and 5 h), hypotonic solution (distilled water or 0.075M KCl solution)/exposure duration (30 min, 1, and 2 h), the time of cell suspension preparation (at hypotonic treatment or before slide preparation) and chromosome aging period (0, 3, and 7 days in Carnoy's fixative). In addition, the type (i.e., fin, gill or kidney) and the amount of tissue (10, 50, 100 or 150 mg) were also investigated. Regardless of the species, the result obtained showed that well-spread chromosomes could be obtained using the following optimized protocol: Juveniles are injected with 0.05% colchicine (at one ml kg-1) and allowed to swim for 3 h. Then, 50 mg of gill tissue is made into cell suspension in 0.075M KCl for 1 h. The cell suspension is treated in Carnoy's fixative (changed three times at 20 min interval) and then aged for 3 days. Finally, chromosome slides are made and stained with 10% Giemsa for 1 h.
Twenty-five traditional and thirty-four geometric morphometric comparisons were carried out on pure and reciprocal crosses of Pangasianodon hypophthalmus (Sauvage, 1878) and Clarias gariepinus (Burchell, 1822). Thirty fish samples each of the C. gariepinus (CH), P. hypophthalmus (PH), Pangapinus (♀PH × ♂CG) and the two distinct morphotypes of the Clariothalmus (♀CG × ♂PH) (Clarias-like and Panga-like) between the ages of four and six months were used for this study. Phenotypically, the Clarias-like Clariothalmus and the Pangapinus progenies were indistinguishable from their maternal parents while the Panga-like Clariothalmus was a phenotypic intermediary of the putative parents but looks more closely to the paternal parent. Hence, both univariate proportion and multivariate analysis of the collected data successfully separated the different fishes into three multivariate spaces. The analysis of the dendrogram with complete linkage and Euclidean distance further showed the close relationship of the isolated Panga-like Clariothalmus progenies to the paternal parent, however, Clarias-like Clariothalmus and the Pangapinus were completely intermingled with their maternal parents. The most important index of discrimination of these fishes into different multivariate spaces was the fin characteristic which showed 100% exclusive ranges for the individual groups in many cases.
The king of rivers or mahseer comprises three genera: Tor, Neolissochilus, and Naziritor, under the Cyprinidae family. The Tor genus has been classified as the true mahseer due to the presence of a median lobe among the three genera. The Tor species are widely distributed across Southeast (SE) Asia, and 13 Tor species have been reported previously: Tor ater, Tor dongnaiensis, Tor douronensis, Tor laterivittatus, Tor mosal, Tor mekongensis, Tor putitora, Tor sinensis, Tor soro, Tor tambra, Tor tambroides, Tor tor and Tor yingjiangensis. However, the exact number of valid Tor species remains debatable. Different and unstandardized approaches of applying genetic markers in taxonomic identification and morphology variation within the same species have further widened the gap and ameliorated the instability of Tor species taxonomy. Therefore, synchronized and strategized research among Tor species researchers is urgently required to improve and fill the knowledge gap. This review is a current update of SE Asia's Tor species, outlining their distribution, morphology, and genetic identification. In addition, the present review proposes that there are ten valid Tor species in the SE Asian region. This list will serve as a template and standard to improve the taxonomy of the SE Asian Tor species, which could serve as a basis to open new directions in Tor research.