Effects of C-N ratio on growth, survival and proximate composition of Macrobrachium rosenbergii post larvae reared under a corn starch based zero-exchange brackish water biofloc system

A 3-week nursery phase for giant river prawn, Macrobrachium rosenbergii post larval (PL), was conducted in biofloc systems at increasing carbon-nitrogen (C-N) ratios of 10:1 (C-N10), 15:1 (C-N15), 20:1 (C-N-20) and 25:1 (C-N25) versus a clear water system (40% water exchange every 2 days and no additional carbon). A total 400 PLs (15.90 +/- 1.29 mg) were cultured in tanks (100 L) filled with brackish water (12 parts per thousand), and corn starch was the carbon source. Growth, survival, feed conversion ratio (FCR), whole body proximate composition, water quality parameters, biofloc volume, zooplankton and proximate composition were measured. Total ammonia nitrogen (TAN) and nitrite nitrogen (NO2-N) were significantly lower in all biofloc systems as well as containing increased zooplankton groups (ciliates, rotifers and nematodes). Specific growth rate (SGR) was similar between the control (9.29 +/- 0.35% day(-1)) and the CN-20 (9.47 +/- 0.18% day(-1)) and CN-25 (9.34 +/- 0.20% day(-1)) treatments; however, SGR significantly declined in the C-N10 treatment (8.03 +/- 0.10% day(-1)). Survival was unaffected by treatments while a higher survival (87.34%) was in CN-20 and it was followed by CN-25 (80.34%), control (80.33%), CN-10 (77.0%) and CN-15 (76.66%) respectively. The best FCR was in the C-N20 treatment at 2.65, but was not statistically different than the control at 3.12. However, crude protein of the PLs was significantly higher in the C-N15, C-N20 and C-N25 treatments compared with the control. The present findings indicate that the water quality was better managed in the biofloc treatments compared with the control; however, lower C-N ratios of 10 and 15 can negatively impact prawn growth compared with the control or higher C-N ratios of 20 or 25.

Automated summary

The study found that in biofloc systems with different carbon-nitrogen ratios, an increase in zooplankton count led to lower levels of ammonia nitrogen and nitrite nitrogen. This had varying impacts on the growth and survival rates of giant river prawn post larvae, with a C-N ratio of 20 or 25 being most beneficial.