Turkmenistan's TDH official news agency says Niyazov appointed Mukhammet Gurbannazarov as the new governor of the Mary region.
Byashymov, whom Niyazov also ordered to pay 10 months of salary in fines, is the fifth Turkmen regional leader to lose his job since October 25.
Over the past month, Niyazov has dismissed the governors of Turkmenistan's other four regions (Balkan, Ahal, Dashhowuz, and Lebap). He has also sacked several lower-ranking administration and agriculture officials.
The reshuffle is linked to what seems to be a decrease in raw cotton output and the prospect of grain shortages for next year.
The opposition Gundogar information website on November 28 said a total of 52 governors had succeeded one another at the head of Turkmenistan's five regions since 1991.