Effects of high wheat bran input on the performance of a biofloc system for Pacific white shrimp (Litopenaeus vannamei)

Applying an external carbohydrate source to stimulate heterotrophic bacteria growth in biofloc systems is a common practice which could be simplified by combining the carbohydrate source with the feed into one pellet. In the current study, such an approach was tested in Pacific white shrimp, Litopenaeus vannamei. Wheat bran (WB) containing non-starch polysaccharides (NSP), a hardly digestible carbohydrate, was mixed with a commercial-like shrimp diet (control; CONdiet) to create a wheat bran rich diet (WBdiet). Shrimp were fed isonitrogenously, resulting in the WBdiet group receiving equal absolute amount of nitrogen but more carbon than the CONdiet group. A digestibility trial was performed in a clear-water recirculating aquaculture system for 35 days, using 6 replicates aquaria per diet. Compared to the CONdiet, shrimp fed with the WBdiet had a reduced overall digestibility and an increased faecal carbon to nitrogen ratio (C:N ratio) from 12 to 20. Following the digestibility trial, a second experiment was performed to monitor the growth performance of the shrimp reared in biofloc systems for 42 days, using three replicate tanks per diet. The dissolved nitrogen species concentration was lower in the tanks fed the WBdiet, while the dissolved carbon concentration was similar between the diets. From a system perspective, similar amounts of nitrogen accumulated across the system compartments with both diets, with maximum 3% total nitrogen loss reached at the end of the experiment. The percentage of carbon loss per kg feed was similar between diets. Overall, diluting the CONdiet with wheat bran and feeding both diets isonitrogenously did not reduce shrimp survival and had minor effect on growth (2% reduction of the specific growth rate). Therefore, incorporating NSP-rich ingredients, such as wheat bran applied as one pellet has a potential to simplify the carbon addition management in a biofloc system.