Intensive nursery production of the Pacific white shrimp Litopenaeus vannamei using two commercial feeds with high and low protein content in a biofloc-dominated system

•Litopenaeus vannamei PL were fed low (LP30) and high (HP40) protein diets in limited exchange nursery raceways.•Molasses prevented significant accumulation of NH3 but not NO2 in the culture medium.•The HP40 treatment had higher NO2, NO3 and PO4 than the LP30 treatment.•Shrimp fed HP40 had higher growth than those fed LP30, with no difference in survival or PER.•Lower protein feed may improve water quality, reduce feed cost and environmental impact. The efficiency of shrimp production in limited exchange systems can be improved by optimizing the protein content of the feed. Therefore, a 62-d nursery study was conducted with 10-day-old Litopenaeus vannamei postlarvae stocked (5000PL10m−3) in four 40m3 raceways to evaluate the effect of high (40%) and low (30%) crude-protein (HP40 and LP30, respectively) diets and molasses supplementation on selected water quality indicators and shrimp performance under limited water exchange. Each raceway was equipped with a real-time dissolved oxygen monitoring system and a foam fractionator to control particulate matter. The level of molasses used in this study was effective in preventing significant ammonia accumulation in the culture medium. However, these supplementation levels were not effective in preventing nitrite accumulation. The HP40 treatment had significantly higher nitrite, nitrate and phosphate concentrations than the LP30 treatment. Shrimp mean final weight (0.94 vs. 1.03g) and specific growth rate (SGR) (11.03 vs. 11.19% day−1) were significantly different between treatments (P0.05). The data suggest that substituting high-protein (40%) with low-protein (30%) feed in the nursery phase in a biofloc dominated system operated with minimal discharge may provide an alternative to improve shrimp biofloc technology, through improved water quality, cheaper (lower protein) feed and reduced environmental impact.