RESUMO
Pacu (Piaractus mesopotamicus) is a Neotropical fish of major importance for South American aquaculture. Septicemia caused by Aeromonas hydrophila bacteria is currently considered a substantial threat for pacu aquaculture that have provoked infectious disease outbreaks with high economic losses. The understanding of molecular aspects on progress of A. hydrophila infection and pacu immune response is scarce, which have limited the development of genomic selection for resistance to this infection. The present study aimed to generate information on transcriptome of pacu in face of A. hydrophila infection, and compare the transcriptomic responses between two groups of time-series belonging to a disease resistance challenge, peak mortality (HM) and mortality plateau (PM) groups of individuals. Nine RNA sequencing (RNA-Seq) libraries were prepared from liver tissue of challenged individuals, generating â¼160 million 150 bp pair-end reads. After quality trimming/cleanup, these reads were assembled de novo generating 211,259 contigs. When the expression of genes from individuals of HM group were compared to individuals from control group, a total of 4,413 differentially expressed transcripts were found (2,000 upregulated and 2,413 downregulated candidate genes). Additionally, 433 transcripts were differentially expressed when individuals from MP group were compared with those in the control group (155 upregulated and 278 downregulated candidate genes). The resulting differentially expressed transcripts were clustered into the following functional categories: cytokines and signaling, epithelial protection, antigen processing and presentation, apoptosis, phagocytosis, complement system cascades and pattern recognition receptors. The proposed results revealing relevant differential gene expression on HM and PM groups which will contribute to a better understanding of the molecular defense mechanisms during A. hydrophila infection.
RESUMO
The pacu (Piaractus mesopotamicus) is a Neotropical fish with remarkable productive performance for aquaculture. Knowledge of genetic resources in Neotropical fish is essential for their applications in breeding programs. The aim of this study was to characterize the genetic diversity of seven farmed populations of pacu which will constitute the basis for a broodstock foundation for coming breeding programs in Brazil. Analysis of one wild population (Paraná River) was used as a reference to compare genetic parameters in the farmed populations. The analyses were performed using 32 single-nucleotide polymorphisms (SNP) and 8 simple sequence repeat (SSR) markers. No significant differences in genetic diversity between populations estimated through the number of alleles and allelic richness, observed heterozygosity, expected heterozygosity, and minimum allele frequency were detected (p > 0.05). Low genetic diversity was observed in all farmed stocks and the wild population. Moreover, we detected low genetic structure when comparing farmed and wild populations for SNPs (FST = 0.07; K = 3) and SSRs (FST = 0.08; K = 2). Analysis of molecular variance (AMOVA) demonstrated that genetic variation was mostly within populations. Kinship analysis showed that most fish farms included related individuals at a proportion of at least 25%. Our results suggest that the basal broodstock for pacu breeding programs should be founded with individuals from different fish farms for higher genetic diversity and to avoid inbreeding risks.