Genetic differentation between Penaeus kerathurus and P. japonicus (Crustacea, Decapoda)

Genetic differentiation and variability data have been obtained by electrophoretic analysis of 2 species of prawns (Penaeus kerathurus and P. japonicus).Both are fished commercially and used in either commercial or experimental aquaculture systems.Genetic distance calculated according to Nei's method (D = 0.887) shows the 2 species to be very different genetically.Similar values have frequently been found in other animal groups between congeneric species that are phylogenetically distant or between species in different genera.The contribution of different loci to the genetic distance, with respect to their metabolic role, is briefly discussed.Variability estimates for the 2 species differ cons~derably.In P, japonicus, mean heterozygosity expected at equilibrium (He) is 0.121; mean number of alleles per locus (A) is 1.484, and frequency of polymorphic loci (P) is 0.387.Respective values for P. kerathurus are Fie = 0.055, A = 1.265 and P = 0.265.Stochastic and deterministic factors that may possibly explain high heterozygosity in P. japonicus are hypothesized.Future research requires natural populations to be examined.