How do largemouth bass determine sex?

The mechanism that determines sex in largemouth bass is unknown.  Within fishes various genetic systems, from polygenic to heterogametic, and environmental systems, from temperature dependent to social interaction, have been documented.  We used amplified fragment length polymorphisms of genomic DNA and the distribution of dominant genetic markers to evaluate possible sex determining systems in largemouth bass.  A total of 64 primer combinations produced 2315 scorable polymorphic markers between equal groups of males and females (n=14 each) from two families.  Forty-three of these markers were observed with significantly different frequencies between groups (Fisher exact test, α = 0.001) and all occurred more frequently in females than males.  The number of sex biased markers observed (43) is greater than the number expected by chance (2 to 3), however, no marker was fixed in one group and absent from the other.  The results suggest a genetic rather than environmental component to sex determination in largemouth bass.  Our findings do not support the presence of typical heterogametic sex chromosomes but are consistent with the presence of small hemizygous regions carried autosomally or on evolutionarily young sex chromosomes in females.