John Rush Gold

Nuclear‐encoded microsatellites and mitochondrial DNA (mtDNA) sequences were assayed from Cobias Rachycentron canadum sampled in waters offshore of Virginia (U.S. Atlantic), Mississippi and Louisiana (Gulf of Mexico), and Taiwan (Southeast Asia). Global exact tests and analysis of molecular variance revealed that Cobias from U.S. waters were homogeneous for alleles and genotype distributions at 27 nuclear‐encoded microsatellites and were homogeneous in mtDNA haplotype distribution, whereas both genetic markers in Cobias from Taiwan differed significantly from those of Cobias in U.S. waters. Based on these genetic differences, use of Cobia broodstock from Southeast Asia in U.S. aquaculture facilities is not recommended. Results are compatible with the use of Cobia broodstock from either the U.S. Atlantic or the Gulf of Mexico for aquaculture at U.S. facilities; caveats to the exchange of broodstock between these two regions are discussed.

Genetic variation and divergence among samples of Chilean hake Merluccius gayi, from three localities off the coast of Chile and one locality off the coast of northern Peru, were assessed using sequences from the control region of mitochondrial DNA. Homogeneity tests revealed occurrence of at least three distinct genetic stocks of M. gayi within the region sampled. Factors potentially contributing to genetic divergence among M. gayi probably include hydrodynamics and behaviour.

Population structure of lane snapper Lutjanus synagris in U.S. waters in the northern Caribbean Sea was assessed using nuclear‐encoded microsatellites and mitochondrial DNA (mtDNA) from samples from four localities in the U.S. Caribbean and one locality in the Florida Keys. Significant heterogeneity was detected for both allele and genotype distributions (microsatellites) and for haplotype distribution (mtDNA). Pairwise comparisons revealed that fish in the Florida Keys differed significantly from fish in the U.S. Caribbean with respect to both microsatellites and mtDNA. A parsimony network of mtDNA haplotypes was consistent with division of the five sample localities into two distinct populations. Genetic diversity at both microsatellites and mtDNA was greater among fish from the Florida Keys. The average, long‐term migration rate from the U.S. Caribbean westward to the Florida Keys was approximately 1.75‐fold greater than the reverse, suggesting that the elevated genetic variability among fish from the Florida Keys reflects the westward movement of alleles as a function of westward‐flowing surface currents in the region. Bayesian coalescent analysis (microsatellites) indicated that each of the two populations has experienced a 10‐fold decline in effective population size (N_e). Estimates of long‐term effective size, generated using a coalescent, maximum‐likelihood method, were 1,671.9 (Florida Keys) and 2,923.2 (U.S. Caribbean). Estimates of contemporaneous effective size, generated using a linkage‐disequilibrium approach with minor alleles (those with frequencies of 0.02 or less) being excluded, were 275.6 (Florida Keys) and 668.9 (U.S. Caribbean) and differed significantly from one another. Because the samples contained mixed cohorts, the short‐term estimates reflect the effective number of breeders (N_b) that produced the cohort(s) from which the samples were taken. The difference between the long‐term and short‐term estimates of N_e (or N_b) suggests that the declines in the effective size of both populations are relatively recent and that management concern over lane snapper in the Florida Keys is justified. Received July 23, 2010; accepted December 14, 2010

Parentage analysis, employing five hypervariable microsatellite markers, was used to follow spawning patterns of red drum Sciaenops ocellatus broodfish in two spawning tanks through most of a calendar year in a marine fish hatchery dedicated to stock enhancement. Five of six dams and all four sires spawned at least once during the year. Variation in dam and sire spawning incidence and in number of progeny produced per dam and per sire translated into reduced genetic effective size (N_e) per spawn by 40·6% in one tank and 50·8% in the other.

Twenty nuclear‐encoded microsatellites from a genomic DNA library of cobia, Rachycentron canadum, were isolated and characterized. The microsatellites include two tetranucleotide, one trinucleotide, three combination tetranucleotide/dinucleotide, nine dinucleotide, and five imperfect (dinucleotide) repeat motifs. Gene diversity ranged between zero to 0.910; the number of alleles among a sample of 24 fish ranged from one to 15. Cobia support an important recreational fishery in the southeastern United States and recently have become of interest to aquaculture. The microsatellites developed will be useful tools for studying both population genetics (e.g. stock structure, effective population size) and inheritance of traits important to aquaculture.