Effect of carbon and nitrogen ratio (C:N) manipulation on the production performance and immunity of Pacific white shrimp<i>Litopenaeus vannamei</i>(Boone, 1931) in a biofloc‐based rearing system

A 16-week indoor culture trial was conducted to evaluate the effect of varying C:N ratio on growth performance, physico-chemical parameters, microbial dynamics, feed utilization, and immunological parameters. The experiment comprised of five biofloc treatment groups (with varying C:N ratio 5:1, 10:1, 15:1, 20:1) and a control with three replicates each, having 100 nos/m3 as stocking density in 500 L tanks with constant aeration. The C:N ratios of the treatments were manipulated using molasses as an organic carbon source whereas there was no carbon source added in control. The water quality parameters monitored throughout the experiment were found to be within permissible limits in shrimp culture. At the end of the experiment, it was observed that there were significant differences between the treatment groups and the control regarding absolute growth, SGR, FCR, PER, and FER. Furthermore, a considerable difference in immunological parameters, namely, THC, phagocytosis, and PO activity (17.5 × 106 cells per ml, 43.5%, 0.112 Units min−1 mg min−1), was recorded among the treatments compared to that of the control groups (6.2 × 106 cells per ml, 31.5%, 0.051 Units min−1 mg min−1) respectively. Enhanced growth and survival with substantial disease resistance were recorded in C15 treatment. The results indicate that the CN15 ratio coupled with minimal water exchange is optimal for improved survival, growth, and immune activity.