ABSTRACT. Tambaqui (Colossoma macropomum) is the main fish species farmed on a commercial scale in northern Brazil. In view of the current scenario of Brazilian aquaculture, studies on the genetic improvement and reproductive management of captive tambaqui are crucial in identifying the genetic variability of broodstocks and devising management practices. Genetic diversity of three tambaqui broodstocks in western Amazon was evaluated using molecular markers. Fin samples were collected from 89 fish; 38 from Balbina, 30 from a hatchery in Rio Preto da Eva, and 21 from the experimental farm of the Federal University of Amazonas (UFAM). Ten primers were used for the analysis of diversity and genetic structure. Of the 152 bands produced, 146 were polymorphic. The proportion of polymorphic loci showed little variation among the three stocks. The lowest and highest rates were found in the Rio Preto da Eva (80.92%) and Balbina (85.53%) stocks, respectively. Heterozygosity (H) and Shannon (I) indices were similar among the stocks; the lowest values were found in Balbina (H = 0.279 and I = 0.419), and the highest in UFAM (H = 0.294 and I = 0.439). Following analysis of the genetic structure and relationship, the sample was divided into two groups, with the Balbina stock clearly deviating from the others. The results suggest that, to increase genetic variability, molecular information may be used instead of replacement of wild breeders. The groups characterized here can be used in genetic improvement programs with other tambaqui broodstocks from different areas of South America.
The aim of this study was to molecularly identify different species of Aeromonas isolated from farmed tambaqui (Colossoma macropomum) from North Brazil, and evaluate their pathogenic potential by the presence of virulence genes. From the extraction of bacterial DNA, PCR (polymerase chain reaction) of the primers 16S rDNA, aerA (cytolytic enterotoxin), ast (cytotoxic enterotoxin) and act (cytotoxic enterotoxin) were performed. Of 24 isolates evaluated, eight amplified the ast gene, one amplified the act gene, but the areA gene was not amplified in any isolate. Sequencing of the 16S rRNA primer revealed a predominance of Aeromonas jandaei specie (92%). Aeromonas taiwanensis (4%), for the first time isolated from fish in Brazil, and Aeromonas hydrophila (4%) each appeared as just one isolate. Results showed that 32% of Aeromonas isolated from farmed tambaqui have considerable pathogenic potential for systemic damage, since the selected PCR primers are encoding the most common virulence genes in Aeromonas with high pathogenic intensity.
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