These systems yield 450±
2200 kg ha±1 per 8±10 months (Edwards 1987). In
Malaysia's Krian area, T. pectoralis yields of 135±
470 kg ha±1 were obtained in extensive single rice
cropping systems (Heath 1934; Soong 1948;
Schuster 1955; Tan 1973). In Vietnam's Mekong
Delta, T. pectoralis is only grown in the coastal area,
where farmers grow one traditional rain-fed rice
crop a year owing to salinity problems, water levels
are high, and fertilizer and pesticide inputs are low
(Lazard & Cacot 1997; Duong et al. 1998). In these
systems ®sh yields amount to » 90 kg ha±1 (Duong
et al. 1998).