2.1. Water supply
Each tank was filled with 640 L of tap water and
aerated continuously with two circular air stones (3 L
min1). The characteristics of water supply were the
following: aged tap water: pH 7.17; Ec=0.16 mmhos;
Ca=5 mg L1; Mg=2, 5 mg L1; K=0.00041 mg L1;
P=0.00031 mg L1; Fe=0.578 mg L1; Mn=0.033 mg
L1; Zn=0.00015 mg L1, and Cu=0.00013 mg L1.
2.2. Feed and feeding
The feed was a commercial diet floating pellet
(Car-gill Company) with 24% protein, 6% fat, 6%
fiber, and 11% moisture. The fish were fed twice a
day ad libitum at 09:00 and at 13:30 h. The mineral
content of feed was measured before initiation of
the study. The characteristics of feed are given in
Table 1.
2.3. Sampling and water quality measurement
Dissolved oxygen (DO) and water temperature (T)
in fish rearing tanks were measured twice a week by
YSI Model 57 meters. Electroconductivity (EC) was