Effect of Protein Intake on Growth and Nutrient Retention of Pacific White Shrimp ( <i>Litopenaeus vannamei</i> ) in a Green Water Recirculating Aquaculture System

Feed management and the nutrient content of the diet are two of the most important factors in shrimp culture, as feed makes up around 60% of the total variable costs. Given the cost of protein and its effect on growth, it is critical to understand the effects of both dietary protein and feeding rates on shrimp performance. Hence, the aim of this study was to evaluate the effect of different protein intake levels on growth performance, nutrient retention efficiency, and whole-body composition of Pacific white shrimp (<i>Litopenaeus vannamei</i>) using different levels of crude protein (CP). This was done by feeding four practical diets with 40%, 35%, 30%, and 25% of CP, which were fed at two different rates, one of them being the standard feed rate (100%) and a second adjusted rate to match the protein supplied (40% protein equivalence), resulting in a total of eight treatments with four replicates each. The total ration for each of the treatments was spread out into four feedings per day. Juvenile shrimp (0.41 ± 0.01 g) were stocked into a green water outdoor recirculating system with 32 circular tanks at a density of 30 individuals/tank and reared for 11 weeks. A recirculating aquaculture system (RAS) with green water (~30°C) was used for this trial, which consisted of a central reservoir (⁓1000 L) and treatment tanks (⁓800 L). At the end of the trial, growth performance parameters including final weight, weight gain (WG), biomass, and feed conversion ratio (FCR) were found to be significantly different among treatments (<i>p</i> < 0.05). Average survival was between 94% and 98% for all the treatments. All final body composition values (dry matter, CP, and minerals) did not show significant differences between treatments except for fat (<i>p</i> < 0.05). However, feed utilization measurements including apparent net protein retention (ANPR), and phosphorus retention (PR) showed to have significant differences (<i>p</i> < 0.01), ranging 49%-66% and 16%-27%, respectively. The results from this study demonstrated that treatments with higher protein intake resulted in the best growth performance, meanwhile treatments with lower protein intake had the highest nutrient retention values.