Abstract
The genetic variation in two farmed strains (F3-Panama and F17-Venezuela) of the shrimp Litopenaeus vannamei was examined based on DNA multiloci analyses. Eighteen adults of each strain were analyzed by PCR using a set of VNTR core sequence primers. Genetic similarity, mean allele frequency, mean heterozygosity and the frequency of polymorphic loci were determined for both strains. A dendrogram of genetic similarity was produced by UPGMA clustering. The results for three primers (INS, M13, YN73) revealed different levels of genetic variation within the strains. The higher genetic similarity seen within strain F17 was apparently related to inbreeding, although a bottleneck effect could not be discarded. The low level of genetic variability of this strain could account for the reduced adaptive advantage of these animals and their inability to adjust to breeding conditions in Brazil.
Highlights
Marine shrimp farming in Brazil has increased since the introduction of the species Litopenaeus vannamei from the Pacific Ocean
Electrophoretic analyses using the primers YN73, INS and M13 provided reliable, distinct multiloci band profiles for the two strains (Figure 1); no PCR products were obtained with PER1 and YNZ22
L. vannamei is one of the main marine shrimp species used in commercial farming worldwide, especially in the American continent (Guerrelhas, 1997)
Summary
Marine shrimp farming in Brazil has increased since the introduction of the species Litopenaeus vannamei from the Pacific Ocean. There are about 500 shrimp farms throughout Brazil, in the northeastern region, with nearly 100% of all reared shrimp being L. vannamei (ABCC, 2002). Bottleneck effects, often produced by the reduced number of broodstock used in each generation, can lead to decreased genetic variability and to the loss of rare alleles at certain loci (Perez and Romero, 1991). Inbreeding progressively reduces the genetic variability and this can lead to a decrease in the mean size of the shrimps or to incomplete embryo development (Sunden and Davis, 1991). A close relationship between reduced genetic variability and a decline in spawning capacity has been reported for Marsupenaeus japonicus (Sbordoni et al, 1986)
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