MFSc

The effect of various concentrations of calcium in freshwater on growth, survival,
food intake and food conversion ratio of M. rosenbergii post larvae were investigated in
order to arrive at the optimum range of calcium required in freshwater for successful culture.
In two stage-designed experiment, the first experiment was bioassay for three days, in
order to understand maximum and minimum tolerance level of calcium and magnesium. The
Le-50 of calcium and magnesium in freshwater was found to be 1562.85 and 7823.48 mg/l,
respectively. Based on the results of bioassay, the rearing experiment was carried out in
circular fiberglass tanks for calcium alone. The levels used were 5, 10,20,50, 100,200,300,
400, 500, 600, 700 and 800 mg/l, i.e. 12 treatments and for each treatment two replication
were used. Growth was maximum at 400 mg/l of calcium in freshwater. Better food
conversion ratio and survival were also obtained at this level.
The growth declined in lower and higher concentrations of calcium, but the survival
remained above 80% up to 400 mg/l and later on it got reduced as the concentration of
calcium increased. The food conversion ratio increased at lower and higher levels of calcium.