The efffect of total alkalinity on metamorphosis and growth performance of postlarvae of the giant freshwater prawn (Macrobrachium rosenbergii)

Abstract

This study aimed to determine appropriate alkalinity level for the growth and survival rates of postlavae (PL) of giant freshwater prawn (Macrobrachium rosenbergii). There were four different alkalinity concentrations 60, 90, 120 ppm and the control (about 40 ppm) via two experimental designs. One was set up using cups (one individual/cup, to the total of 30 cups/alkalinity treatment) to examine the molting process, survival and growth rates. The other one was with tanks (12 culture tanks with 100 PL/tank) to test the survival and growth rate. After 42 days of culture, PL underwent 4-5 times of molting and the molting period varied from 6.21 to 10.59 days in each molting event. Results showed that total alkalinity strongly affected all the observed parameters. At 120 ppm alkalinity, M. rosenbergii had significantly shorter molting period and higher molting rate than those grown at other alkalinity levels (p<0.05). In the cups, total length and specific growth rate of shrimp at alkalinity concentration 120 ppm were significantly higher than those at other treatments (p<0.05) while in the tanks there were no differences among all treatments (p>0.05). However, observing the tanks, the PL at 120 ppm were the most uniform in size and had higher survival rate than those grown at the control treatment (p<0.05). Therefore, we suggest that alkalinity at 120 ppm should be applied in nursing PL of M. rosenbergii for growth improvement. Keywords: Macrobrachium rosenbergii Giant freshwater prawn Alkalinity Molting Growth rate