Coryphaena hippurus Linnaeus, 1758 is a commercial fish which inhabits the epipelagic zone of the oceans. Its distribution is restricted to tropical and subtropical regions. Fisherman from Cabo Frio/RJ identify two morphotypes in the...
moreCoryphaena hippurus Linnaeus, 1758 is a commercial fish which inhabits the epipelagic zone of the oceans. Its distribution is restricted to tropical and subtropical regions. Fisherman from Cabo Frio/RJ identify two morphotypes in the species known as dourado and palombeta which have different value in the market. Moreover, due to overexploitation affecting part of the Brazilian fish stocks, the definition of the taxonomic status of these morphotypes becomes relevant to management of the species. In this work, the taxonomic status of C. hippurus morphotypes was genetically investigated. One hundred and seventeen individuals of Coryphaena hippurus (thirty-two dourados and eighty-five palombetas) arrived at Cabo Frio/RJ between November/2013 and April/2014 were used for allozymes analysis. The loci selection was made by factorial empiric tests (tissue X enzyme X buffer) using discontinuous lithium hydroxide pH 8.0 (TLiOH) buffer. Thirty enzyme systems were tested against five tissues (muscle, liver, heart, gonads and eye), providing interpretable results for nineteen gene loci (-Est-1, -Est-2, -Est-3, -Est-1 , -Est-2, -Est-3, G6pd, Ldh, Mdh-1, Mdh-3, Me-1, Me-2, Odh-1, Odh-2, Pgi, Pgm, Sod, Sordh and Xod) in muscle, liver and gonads. Data analysis was done using the software GENEPOP 4.2, BYOSIS-2, Fstat 2.9.3.2. and PAST 2.08. Results were in the form of gene frequencies, percentage of polymorphic loci, effective number of alleles per locus, expected and observed heterozygosity, inbreeding rates (f, and F), genetic identity and a principal component analysis (PCA). The absence of diagnostic loci, high value of genetic identity (0,935) and inferred number of migrants per generation (3,083) added to no significant values of inbreeding point to genetic homogeneity of the two morphotypes, indicating that they probably are populations of the same species. However, significant differences in heterozygosity and effective number of alleles between morphotypes and also significant deviations from Hardy-Weinberg equilibrium for four loci indicates a possible role for natural selection in shaping patterns of genetic variation in the species. This is especially true for Odh-1 locus, which shows deviations for both morphotypes. This enzyme has been described in the literature as having activity related to glucose metabolism and it may be involved with explosive swimming. Then it is possible to hypothesized that differential mortality can explain the differences in frequency observed for this locus in dourado (probably the adults of C. hippurus) and palombeta (probably the young individuals of the species). However, the evidence found in this work are not enough to contra pose the neutralist explanation that the pattern observed is purely due to chance. The conundrum of selectionist explanations is it lack of parsimony. Other molecular markers, more samples, ecological data and specific tests for the natural selection hypothesis are necessary before it can be better supported.