Application of enzyme-hydrolyzed cassava dregs as a carbon source in aquaculture

Highlights: • High yield of reducing sugar was produced by enzyme hydrolysis of cassava dregs. • Enzyme-hydrolyzed cassava dregs as a substitute of sucrose applied in biofloc aquaculture system. • Enzyme-hydrolyzed cassava dregs was more easily assimilation by heterotrophic bacteria. • Microorganism in biofloc will affect the indigenous microflora in shrimp intestines. As a kind of tropical agricultural solid waste, cassava dregs had become a thorny nonpoint source pollution problem. This study investigated the feasibility of applying cassava dregs as a substitute for sucrose in biofloc technology (BFT) systems. Three types of biofloc systems (using three different carbon sources sucrose (BFT1), cassava dregs (BFT2) and enzyme-hydrolyzed cassava dregs (BFT3) respectively), and the control were constructed in this experiment in 200 L tanks with a C/N ratio of 20/1. The comparison of the water quality indicators (The total ammonia nitrogen (TAN), nitrite (NO₂⁻-N), nitrate (NO₃⁻-N), chemical oxygen demand (COD)), biofloc for the above four groups was performed, and the results indicated that BFT3 showed greater potential to the formation of biofloc, which was beneficial for the water quality control. So the shrimp survival rate was the highest and the feed conversion rate was the lowest in BFT3. Besides, the high-throughput sequencing results showed that the relative abundance of heterotrophic bacteria in the top 30 dominant microbial communities in BFT3 was higher than those in BFT1 and BFT2 by 20.70% and 1.19%, respectively, which could decrease TAN to improve the water quality. Overall, the results had proved that the cassava dregs of enzymes hydrolysis could be used as an ideal and cheap carbon source in BFT.