An investigation into the population structure of white seabass (Atractoscion nobilis), in California and Mexican waters using microsatellite DNA analysis.

Abstract

            Sport and commercial landings of white seabass have declined, particularly in southern California, and populations now appear to be severely impacted. To provide information critical to the management of this species, the population structure was analyzed using microsatellite DNA analysis of genomic (total) DNA. This genetic data was used to compare white seabass collected throughout the species range to: 1) determine the structure of the populations; 2) estimate and analyze gene flow within and among seabass populations; 3) evaluate heterozygosity within populations; and, 4) identify genetic markers distinguishing hatchery-bred individuals from wild-type individuals.

            A total of 539 fish was collected from Pacific and Mexican waters from 1990-1995. An additional 150 samples were provided by Hubbs Research Institute. Twelve samples were chosen at random from each of nine region across the entire range of the species, and 12 others from the Oxnard grow-out facility. Samples were collected from Pt. Conception to Magdellena Bay in the Pacific, and from the northern Gulf of California, from Baja. Total genomic DNA was extracted from all individuals. Five seabass were selected at random for probe production. Microsatellite DNA from eight polymorphic loci was used detect and analyze microsatellite data for each of the random samples..

            The eight genetic loci used in this study consisted of one dinucleotide and seven trinucleotide repeats. These ranged from as few as three alleles to as many as 34, for an average of 11.25. For any given set of seabass, the average number of alleles was lower, with the minimum number of alleles being present in the Oxnard grow-out facility (avg = 5). Expected heterozygosity values for the loci ranged form a low of 0.26 to a high of 0.95 in the total sample, with varying values among sampled regions. Nei's genetic distance and G-statistics (Gst) calculated from pairwise comparisons from the ten sampled regions. These values ranged from a high of 0.047 to a low of 0.0031. The Baja groups showed greater genetic distances, than did the southern California Bight groups. The probability of any two animals being identical for all loci was calculated for these samples. The values range from a low of 2x10-9 to a high of 7x10-7. The average value for seabass sample as whole was 1x10-8.

            I determined that it was not possible to identify discrete subpopulations of seabass. It was possible to identify hatchery reared seabass from natural stocks, so it will be possible to create genetic markers for captive breeding program.