Three different C: N ratios for Pacific white shrimp, Penaeus vannamei under practical conditions: Evaluation of growth performance, immune and metabolic pathways

A 28-day experiment was carried out to evaluate different C/N ratios (10:1, 15:1 and 20:1) on growth performance, water quality, survival rate and gene expression related to metabolic pathways of Penaeus vannamei in a biofloc system. To maintain the C/N ratio of the feed input, different carbon sources (molasses, rice bran and wheat flour) in combination were applied after fermentation for a day with biofloc consortium. Results showed that shrimps reared in C/N 10 (630 mg) and C/N 15 (646 mg) biofloc systems showed significantly (p = .0229 and .0263) higher growth when compared to C/N 20 (528 mg) and control (374 mg). With regard to the production of extracellular enzymes, protease, lipase and xylanase were found predominantly in colonized bacteria isolated from biofloc treatments, whereas amylase was commonly found in all the treatments. The proPO activity was considerably increased in C/N 10 and 15 treatments than C/N 20 and control. The ranges of relative expression levels of potential genes entailed in metabolite pathway like hexokinase (HK- 6.57-8.17), pyruvate kinase (PK-5.79-7.96), crustacean hyperglycaemic hormone (CHH- 6.99-7.66) and fatty acid synthase (FAS- 6.57-8.86), triacylglycerol lipase (TGL-6.99-8.66) and immune gene (Toll receptor- 4.57-4.86) fold up-regulated expression were observed in the biofloc treatments than that of the control. The overall findings indicate that the rearing of P. vannamei shrimp in C/N 10 and 15 biofloc systems could improve the growth performance, water quality and development of immune and metabolic responses.