The first transcriptome sequencing and data analysis of the Javan mahseer (Tor tambra)

The Javan mahseer (Tor tambra) is one of the most valuable freshwater fish found in Tor species. To date, other than mitogenomic data (BioProject: PRJNA422829), genomic and transcriptomic resources for this species are still lacking which is crucial to understand the molecular mechanisms associated with important traits such as growth, immune response, reproduction and sex determination. For the first time, we sequenced the transcriptome from a whole juvenile fish using Illumina NovaSEQ6000 generating raw paired-end reads. De novo transcriptome assembly generated a draft transcriptome (BUSCO5 completeness of 91.2% [Actinopterygii_odb10 database]) consisting of 259,403 putative transcripts with a total and N50 length of 333,881,215 bp and 2283 bp, respectively. A total count of 77,503 non-redundant protein coding sequences were predicted from the transcripts and used for functional annotation. We mapped the predicted proteins to 304 known KEGG pathways with signal transduction cluster having the highest representation followed by immune system and endocrine system. In addition, transcripts exhibiting significant similarity to previously published growth-and immune-related genes were identified which will facilitate future molecular breeding of Tor tambra.

Microsatellite Characterization of Malaysian Mahseer (Tor spp.) for Improvement of Broodstock Management and Utilization

In this study, a mixture of Tor tambra and T. tambroides with unknown genetic background were collected from 11 localities in Malaysia for broodstock development and sperm cryo-banking. This study aims to assess the microsatellite (simple sequence repeat, SSR) variation, genetic diversity, genetic differentiation, level of gene flow, population structure, genetic relatedness and their demographic aspects among these Tor populations, in addition to establishing their SSR profile by employing 22 SSR markers via fragment analysis. Total genomic DNA was extracted from 181 samples (91 cryopreserved milt samples and 90 scale samples of live broodfish). Results showed the Tor spp. collection retained their genetic variation but exhibited excessive homozygosity among individuals within population. Moderate genetic differentiation was shown among the populations, with highly significant (p < 0.001) fixation indices (F_ST, F_IS and F_IT). A low gene flow over all loci (Nm 1.548) indicates little genetic variation transfer between populations. The genetic structures of all the populations were successfully resolved into four main clusters by an unweighted pair group method with arithmetic mean (UPGMA) dendrogram generated based on Nei's genetic distances. The population structures based on principal coordinates analysis (PCoA) and the Bayesian model also suggested four distinct clusters following geographical regions and eight closely related populations. This study provided a useful baseline reference for better genetic management and utilization of the Tor spp. stocks in their breeding and conservation programmes.