BIOLOGY OF OSCILLATORIA CF CHALYBEA, A 2-METHYLISOBORNEOL PRODUCING BLUE-GREEN-ALGA OF MISSISSIPPI CATFISH PONDS

Relative abundance of Oscillatoria cf. chalybea was monitored during May-November, 1993, in 40 ponds at four catfish farms located 50-100 km apart in west central Mississippi, USA. The occurrence of O. cf. chalybea coincided with the period mat water temperatures remained above 20 degrees C. In 70% of ponds, O. cf. chalybea was present for a period of 2-20 weeks. The alga recurred in all ponds where it had been present in 1990 and 1991. The effects of temperature and light availability on growth rate and 2-methylisoborneol (MIB) production of O. cf. chalybea were studied in continuous cultures. At 28 degrees C, maximum specific growth rates were 0.8 d(-1) (24 h light) and 0.6 d(-1) (14 h light:10 h dark). Algal cells contained less MIB when adapted to the shorter light cycle than when grown under continuous light Specific growth rate of O. cf. cholybea dropped from 0.3 to 0.1 d(-1) when temperature was changed from 21 to 19.5 degrees C (14 h light).