Microsatellite analysis of pacu broodstocks used in the stocking program of Paranapanema River, Brazil

Abstract

Monitoring the genetic diversity has fundamental importance for fish stocking programs. This experiment aims to evaluate the genetic diversity in two hatchery stations (A and B) with pacu Piaractus mesopotamicus (Holmberg, 1887) in Andirá, state of Paraná, Brazil used in stocking programs of Paranapanema River. Six microsatellite loci were amplified using DNA extracted from 60 fin-clipping samples. The broodstock B had the average number of alleles and the mean heterozygosity (alleles: 3.7 and H O: 0.628) higher than the broodstock A (alleles: 3.5 and H O: 0.600). Alleles with low frequency levels were observed in the both broodstocks. The positive coefficients of endogamy in the locus Pme2 (broodstock A: F IS = 0.30 and broodstock B: F IS = 0.20), Pme5 (broodstock B: F IS = 0.15), Pme14 (broodstock A: F IS = 0.07) and Pme28 (broodstock A: F IS = 0.24 and broodstock B: F IS = 0.20) indicated deficiency of heterozygotes. Presence of null allele in the locus Pme2 was detected. The negative estimates in loci Pme4 (broodstock A: F IS = - 0.43 and broodstock B: F IS = - 0.37), Pme5 (broodstock A: F IS= - 0.11), Pme14 (broodstock B: F IS= - 0.15) and Pme32 (broodstock A: F IS = - 0.93 and broodstock B: F IS = - 0.60) were indicating the excess of heterozygotes. Evidence of linkage disequilibrium and lower allelic richness was found only in the broodstock A. Nei's gene diversity was high in both broodstocks. The genetic distance (0.085) and identity (0.918) showed similarity between broodstocks, which reflects a possible common origin. 6.05% of the total genetic variance was due to differences among broodstocks. Recent bottleneck effect in two broodstocks was observed. The results indicated a higher genetic diversity in the two broodstocks and they presented low genetic difference. This was caused by the reproductive management in both hatchery stations, reduction of population size and genetic exchange between the hatchery stations.