An elecrophoretic evaluation of bi-subspecific populations of largemouth bass in small impoundments in Texas

Abstract

During 1978-1983, samples of largemouth bass Micropterus salmoides were taken from 10 small impoundments (0.4 to 16.0 hectares) in north-central, south-central, and southwestern Texas and submitted to electrophoretic analysis to determine individual genetic status. These impoundments consisted of seven farm ponds and three U.S. Soil Conservation floodwater retarding structures which had been stocked with northern largemouth bass M. s. salmoides and/or Florida largemouth bass M.s. floridanus in an effort to establish stable populations of both subspecies and the intergrade. Stocking rates varied between ponds and were determined by size of impoundment, fish populations present at time of stocking, and research objectives. Stable intergrading populations did not result from the stocking regimes used in this study. In all populations studied, one subspecies or the other was effectively excluded with the formation of the first year class of largemouth bass. In 8 of 10 populations, northern largemouth bass were dominant, while Florida largemouth bass dominated the remaining two populations. Subspecific domination was the result of combined effects of differential subspecific growth, survival, and reproductive success. As a result of subspecific domination, maximum heterozygosity can only be attained through restocking of the less successful subspecies. Restocking may have to take place at intervals as short as 2 years. Comparisons of growth of northern largemouth bass and F1 intergrades indicated that northern bass attained greater total length at age I. However, F1 intergrades demonstrated significantly faster growth after age I. Total length of F1 intergrades approached or surpassed that of northern largemouth bass at age II. Evaluations of the efficacy of electrofishing and/or angling in attaining representative genetic samples from intergraded populations were conducted in four impoundments. No systematic sampling bias which could be related to discrete genotypes of individuals was found in samples collected using either of these two gear types. Differences between estimates of allele and genotype frequencies and actual population allele and genotype frequencies would not lead to formulation of improper genetic management strategies. Evaluation of the utility of lateral-line scale count as an indicator of genetic status of individuals indicated that this meristic count is of little value. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI