Poly-β-hydroxybutyrate concentration, microbial enzymes activity, and nutritional value in biofloc system using different carbon sources and C/N ratios in common carp, Cyprinus carpio culture

This experiment was designed with three carbon sources (Dextrin, wheat bran, and corn starch), each with two carbon to nitrogen (C/N) ratios (19 and 30) for 4 weeks. The data obtained from two variables (carbon sources, C/N ratio) were analyzed with a two-way analysis of variance. At the end of the experiment, the results indicated that the use of varying carbon sources and C/N ratios significantly changed the nutritional value of microbial flocs (p < 0.05). Also, the results showed that both variables significantly affected the main groups of saturated, mono-unsaturated, and polyunsaturated fatty acids in the microbial flocs (p < 0.05). Dextrin flowing corn starch at a low C/N ratio significantly increased poly-beta-hydroxybutyrate accumulation in microbial flocs (p > 0.05). The microbial enzyme profile changed in all carbon sources but C/N ratios did not affect microbial enzymes in the treatments except in a significantly higher value for amylase and acidic protease activity at a C/N ratio of 30 (p < 0.05). Also, at the end of the experiment, total bacteria and Lactobacillus count were affected by carbon sources and the highest density was observed in wheat bran and Dextrin respectively. These findings may encourage farmers to consider specific carbon sources and C/N ratios based on culture conditions and species requirements.