Avaliação genética do estoque fundador de surubim, Pseudoplatystoma corruscans (Spix & Agassiz, 1829), para o repovoamento do submédio Rio São Francisco

Abstract

The surubim, Pseudoplatystoma corruscans, is one of the most important native fish species in South American hydrographic basins, especially in São Francisco River, where it is considered a top chain predator. Different aspects have contributed to the decline of this species populations, especially at the submedium São Francisco, thus raising the necessity of a restocking program to recover the resource. A basic principle in such programs is that a large number of unrelated wild fish should ideally be used as founders, when possible or, alternatively, a small number of unrelated wild fish with few genetic relatedness could be used. Therefore, the genetic structure of the founder stock constitutes an essencial information to the success of such programs. This project aimed to evaluate the genetic structure of the founder stock of the restocking program of surubim maintained by Chesf in Paulo Afonso city, through the use of microsatellite molecular markers. DNA of 80 breeders were genotyped for 5 different microsatellite markers. PCR products were separated by polyacrylamide gel electrophoresis stained with silver nitrate. Statistical analysis were carried out using GENEPOP software, in which parameters such as number of alleles (A), observed (Ho) and expected heterozygosities (He), Hardy-Weinberg deviation, linkage disequilibrium and inbreeding coefficient (FIS) were calculated. GenAlEx 6.1 was used to calculate the number of effective alleles and relatedness coefficient (rxy). Results showed that the number of alleles ranged between from 6 to 18 and the number of effective alleles, from 3.28 to 9.25. Average observed and expected heterozygosities were 0.63 and 0.84, respectively. All loci, except Pcor5, showed deviation from Hardy-Weinberg equilibrium (P<0,001). Average inbreeding coefficient (FIS) for the 5 loci was 0.24. The analysis of linkage disequilibrium, when corrected by Bonferroni, were significant for loci Pcor21 and Pcor10 (P<0.05). The average relatedness coefficient (rxy) was -0.008 for a total number of 2926 possible pairwise combinations. A great genetic diversity, expressed in number of alleles and in a low value of average relatedness, was obtained despite a deficit of heterozygotes was observed in this stock. Such deficit seems to reflect the strategy adopted in the composition of this stock, in which individuals caught at the medium and lower São Francisco River, separated by two dams, were mixed together. It is feasible to conclude that this founder stock retained genetic diversity comparable to those found in the wild stocks and could be used in a restocking program.