Summary

Description

This study compared the genetic variability of Louisiana mosquitofish at 15 sites in a dioxincontaminated watershed and one site outside the watershed. Allozyme frequencies, determined by starch gel electrophoresis, were used to compare genetic variation. The data suggest that fixation of two loci GPI2 and PGM2 shows the loss of alleles c and a, respectively. Those alleles may be sensitive to effluent contaminants or used as markers for another locus that is sensitive. Similarly, IDHP1 a and ADA1 a are two rare alleles seen in upstream, but not downstream sites; however, ADA1 a also appeared again at the farthest downstream site. Thus, those alleles may be sensitive, though their usefulness for monitoring is questionable due to their rarity. In contrast, GPI1 a and ADA 1 c were found only below the point source effluent, possibly suggesting some level of resistance, or again imp ling the sensitivity of other alleles which confer some level of improved fitness on individuals upstream of the dioxin point source. While allelic shifts or fixation at GPI and IDHP have been frequently related to contaminants in the field or survivorship or sensitivity in laboratory toxicity tests, further investigation is required to elucidate underlying causes due to the relatively small sample size utilized.