Comparing a chemoautotrophic-based biofloc system and three heterotrophic-based systems receiving different carbohydrate sources

• An experiment compared no carbohydrate addition to molasses, sucrose, and glycerol addition.
• There was significantly greater nitrate concentration in systems without carbohydrate addition.
• BOD5 and solids concentration were significantly higher in systems with carbohydrate addition.
• Shrimp performed best in systems with no carbohydrates and in those with added sucrose.

A 56-day study was conducted in which shrimp (Litopenaeus vannamei) were stocked at 300 m−3 into 16, 500-L tanks. Four treatments were created: chemoautotrophic (CA), heterotrophic sucrose (HS), heterotrophic molasses (HM), and heterotrophic glycerol (HG). The heterotrophic treatments were managed such that the C:N ratio of inputs (feed and carbohydrate source) was 22:1. The chemoautotrophic treatment received no added carbohydrate, only shrimp feed. Each treatment was assigned randomly to four replicate tanks. Nitrate-N was significantly greater in the CA treatment, accumulating to a peak mean concentration of 162 mg NO3-N L−1 and nitrate was typically below detection (<0.01 mg NO3-N L−1) in the heterotrophic treatments. 5-Day biochemical oxygen demand (BOD5) was significantly greater in the heterotrophic treatments compared to the chemoautotrophic treatment. Total suspended solids concentration was significantly lower in the CA treatment compared to any other. Shrimp growth rate was significantly greater in the CA and HS treatments versus the HM treatment and there was no significant difference in growth rate between the HG treatment and any other treatment. These results indicate that differences in management and carbohydrate source can lead to substantial disparity in system function and shrimp production.