Effects of C/N Ratio for Bi-Culture of Litopenaeus vannamei (Boone, 1931) and Macrobrachium rosenbergii (de Man, 1879) in a Molasses Based Biofloc System

This study evaluated the effects of different C/N ratios (C10-N, C15-N, C20-N and C25-N, compared to C0-N as control) on growth, water quality, proximate composition, bacterial loads and total haemocyte counts (THCs) of shrimp (Litopenaeus vannamei) and prawn (Macrobrachium rosenbergii) post larvae in a biofloc-based nursery bi-culture system, aiming to optimize C/N ratios for sustainability and production efficiency over 6 weeks. Molasses was used as a carbon source, and water salinity was maintained at 15 ppt. In total, 15 cylindrical plastic tanks (125 L water-holding capacity, 59 cm x 56 cm) were used and filled up each 100 L water for rearing 1500 PL of the two species (750 L. vannamei and 750 M. rosenbergii). At the end of the experiment, significantly higher (p < 0.05) specific growth rate (SGR, % per day) (9.77) and survivability (95.33%) for L. vannamei were recorded in C10-N compared to the other treatments. For M. rosenbergii, the significantly higher (p < 0.05) SGR (% per day) (5.77) was recorded in C25-N, whereas the higher survival rate was found at C10-N (90.67%). The best feed conversion ratio was obtained at C10-N for L. vannamei (1.58), whereas for M. rosenbergii, it was obtained at C25-N (2.43). Significantly the higher (p < 0.05) THCs (L. vannamei = 40.63 x 10(5) and M. rosenbergii = 31.25 x 10(5)) of both species were obtained at C10-N. The experimental C-N ratios led to a significant increase (p < 0.05) in total microbial loads (116.6-355 x 10(9) CFU mL(-1)) compared to the control (18.40 x 10(6) CFU mL(-1)). Moreover, all tested water quality parameters remained within the optimal range across the treatments. The study concluded that a C:N ratio of 10:1 provides the highest economic return, making it the optimal ratio for biofloc-based nursery bi-culture of L. vannamei and M. rosenbergii.