Effect of biofloc volume on growth, survival, economics and proximate composition of Macrobrachium rosenbergii postlarvae cultured in brackish water biofloc system

Biofloc volume refers to the suspended solids in a biofloc system, consisting of bacteria, algae, protozoa, organic matter, and other microorganisms that serve as natural food for cultured fish and crustaceans. Furthermore, optimal biofloc volumes enhance water quality, provide live feed, and improve the overall health of cultured animals. Moreover, excessive biofloc can clog gills, degrade water quality, and reduce animal growth or cause mortality. However, the effects of different biofloc volumes on the production, nutritional quality, and economic viability of culturing giant river prawn, Macrobrachium rosenbergii remain underexplored. Therefore, a 4-weeks experiment was conducted to optimize the suitable biofloc volume of M. rosenbergii postlarvae (PLs). Growth, survival, proximate composition of M. rosenbergii and water quality, total bacteria and zooplankton community were compared among four biofloc (BF) volume groups of BF2 - 5, BF7 - 10, BF12 - 15 ml L−1 and BFZ/zero-solid removal biofloc system. Twelve 125 L polyethylene tanks with water volume of 100 L were used for this experiment. Each tank was stocked with 500 PLs (average initial weight 21.8 ± 2.36 mg). Each treatment was randomly assigned in triplicate. Temperature, nitrite-N and nitrate–N did not differ (P > 0.05) among four treatments. A lower dissolved oxygen concentration was remained (P < 0.05) in the BF-Z than three BF volume treatments. A lower Vibrio spp. density was found (P < 0.05) in the BF2 - 5 than BF12 - 15 and BF-Z treatments. Ciliates, rotifers and nematodes were significantly (P < 0.05) higher in the BF-Z than other biofloc volumes groups. PLs growth was similar (P > 0.05) among four BF volume groups. However, significantly (P < 0.05) a higher survival and economic return were obtained in the BF2 - 5 treatment when compared to those BF7 - 10, BF12 - 15 ml L−1 and BF-Z. In conclusion, our results show that the biofloc volume 2–5 ml L−1 is found suitable for M. rosenbergii PLs, ensuring higher survival and profit in nursery phase can be considered in management practices. • A lower Vibrio spp. density observed in the 2 - 5 ml L-1 floc volume level biofloc system • The floc volume level 2 - 5 ml L-1supported for more prawn postlarvae survival • The best FCR obtained in the 2 - 5 ml L-1floc volume level biofloc system • Simple cost analysis shows a floc volume levels 2 - 5 ml L-1 is economically viable than the floc volume levels of 7 - 10, 12 - 15 ml L-1 and zero-exchange biofloc system when culturing Macrobrachium rosenbergii