Influence of varying dietary protein content on the performance of Pacific white shrimp (Penaeus vannamei) cultured in the biofloc system using low-salinity groundwater of Kuwait desert

Biofloc technology (BFT) is recognized as a sustainable approach to shrimp culture, providing an additional protein source through microbial biomass. This 8-week feeding trial evaluated the effects of varying dietary protein levels on water quality, growth performance, body composition, and physiological responses of juvenile Pacific white shrimp ( Penaeus vannamei ) reared in a BFT system using low-salinity groundwater from the Kuwait desert. Four diets containing 25 % (CP24.7), 30 % (CP29.1), 35 % (CP34.4), and 40 % (CP39.8) crude protein (CP) were formulated. Each treatment was conducted in triplicate using 12 polyethylene tanks (1000 L capacity; 800 L working volume), stocked at 250 juveniles m⁻³ with an mean initial body weight of 0.43 ± 0.00 g. Most water quality parameters (temperature, salinity, alkalinity, pH, dissolved oxygen, total ammonia nitrogen, and nitrate) showed no significant differences among treatments; however, nitrite, settleable solids, and total suspended solids (TSS) differed, with TSS increasing over time. Shrimp fed CP39.8 had significantly higher final body weight (FBW) and average daily growth (ADG) than CP24.7, but no differences were detected among CP29.1, CP34.4, and CP39.8, or among CP24.7, CP29.1, and CP34.4. The CP39.8 also resulted in lower total non-essential amino acid levels than CP24.7. Dietary protein had no effect on saturated fatty acids, though polyunsaturated fatty acids (PUFA) were highest in CP34.4 and lowest in CP39.8. Plasma metabolites and ions varied, with CP24.7 producing higher protein and glucose, while CP29.1 yielded elevated cholesterol and triglycerides. The broken-line regression analysis on FBW and ADG estimated the optimal dietary protein requirement at 33.9 % and 33.8 %, respectively. Considering the response of essential amino acids (arginine and histidine) and fatty acids (EPA and DHA) to graded protein levels, it is suggested that a protein level of 34.4 % is optimal for juvenile P. vannamei reared in low-salinity BFT systems. • Biofloc technology maintained good overall water quality. • A high-protein diet (40 % CP) increased waste and suspended solids. • A low-protein diet (25 % CP) led to reduced growth, poorer nutritional status, and lower lipid metabolism. • The optimal dietary protein level for shrimp in low-salinity BFT was 33.8–34.4 %.