Effects of adding sucrose on Penaeus monodon (Fabricius, 1798) growth performance and water quality in a biofloc system

A 60-day indoor growth trial was conducted to study the effects of biofloc on the growth performance of a Penaeus monodon (Fabricius, 1798), water quality and biological indicators including biofloc volume, chlorophyll-a, heterotrophic bacteria and Bacillus quantity. Two concentrations of sucrose (0 and 75%) were added daily to the P. monodon culture systems (2.94 ± 0.11 g), which were conducted indoors in fibre-glass tanks (500 L). Results showed that the final body weight and weight gain of the adding 75% sucrose group were significantly higher (P < 0.05) than that of the control, as well as significantly (P < 0.05) improved specific growth rates and survival rates, and reduced feed coefficient. Adding 75% sucrose promoted heterotrophic bacteria, Bacillus and phytoplankton reproduction, and significantly (P < 0.05) reduced the concentration of ammonia-N (NH₄-N), nitrite-N (NO₂-N) and nitrate-N (NO₃-N). The changes of water quality indicators in the two groups showed the similar trend at the end of the experiment, and the ammonia-N, nitrite-N, nitrate-N and phosphate-P concentrations in the 75% sucrose group were significantly (P < 0.05) lower than those of the control group, Chlorophyll-a concentrations peaked at 389.12 μg/L in the biofloc sucrose group at 18:00 h, and heterotrophic bacteria peaked 8 h after sucrose was added. The addition of sucrose also reduced the pH of the water. Our research showed that adding sucrose promoted biofloc formation and shortened the formation time; increased the number of heterotrophic bacteria and algae which might play a role in improving water quality by assimilating ammonia-N and other harmful substances in the water; supplemented food for P monodon growth; and reduced the feed coefficient.