Various carbon/nitrogen ratios in a biofloc-based rearing system of common carp (Cyprinus carpio) fingerlings: Effect on growth performance, immune response, and serum biochemistry

Abstract

In this study, three various carbon to nitrogen ratios including 10:1 (C/N-10), 15:1 (C/N-15), and 20:1 (C/N-20) were designed in a biofloc based system with three replicates. The initial biofloc was formed by adding 200 g common carp commercial diet +1 g urea (46% N) + 50 g bottom soil of carp earthen pond. After 56 days, the highest growth indices and the lowest feed conversion ratio were obtained in C/N-20 treatment (P < 0.05). The raised fish in C/N-10 system revealed significantly (P < 0.05) higher serum glucose, alanine aminotransferase, and aspartate aminotransferase compared to other treatments. However, alkaline phosphatase activity was decreased by increasing C/N ratios (P < 0.05). In addition, no significant influence (P > 0.05) was detected in the content of albumin and total protein among the treatments. The level of immunoglobulin M did not change significantly (P > 0.05) in C/N-15 and C/N-20 groups, while it was significantly higher than C/N-10 group (P < 0.05). The mRNA expression levels of interleukin-1 beta, interleukin-8, tumor necrosis factor-alpha, and lysozyme genes were up-regulated with increasing in the C/N ratios. The anti-inflammatory interleukin-10 gene expression was notably suppressed in C/N-20 compared to C/N10 (P < 0.05). Based on our results, the humoral immune parameters, immune-related gene expression, and zootechnical responses were notably ameliorated in common carp cultured in a biofloc system at a C/N ratio of 20:1.