Nutrient value and contribution of microbial floc to the growth performance of juvenile shrimp, Litopenaeus vannamei, fed fatty acid and amino acid-restrained diets under a zero-water exchange intensive system

Abstract

Studies have demonstrated that biofloc can be used as food or as a nutrient source for farmed shrimp, either through direct intake from culture water or as an ingredient. We investigated the nutrient value and contribution of biofloc to the growth of L. vannamei fed essential fatty acid (EFA)- and amino acid (EAA)-restrained diets. A total of 6144 shrimp of 3.04 ± 0.43 g body weight (BW) were reared in 48 outdoor tanks of 1 m3 under 128 animals m−3 and fed 12 diets during 72 days in a biofloc-dominated system. Diets contained 31.54 ± 0.98% crude protein (CP, % dry matter basis) and 7.91 ± 0.46% total lipids. Dietary EFA and EAA were manipulated by progressively reducing the inclusion of fish oil from 2.00 to 1.00 and 0%, and fish meal from 12.00 to 8.00, 4.00, and 0%, resulting in a 3 × 4 fish oil-fishmeal factorial design (diets 2–12, 2–8, 2–4, 2–0, 1–12, 1–8, 1–4, 1–0, 0–12, 0–8, 0–4, and 0–0; % of the diet; as-fed). The relative contribution of biofloc and diets to shrimp growth was estimated using the stable carbon isotope (δ13C) mass spectrophotometry analysis. At harvest, shrimp final survival (79.4 ± 7.3%), yield (1407 ± 125 g m−3), FCR (1.88 ± 0.18), and AFI (20.6 ± 0.3 g of diet stocked shrimp−1) were unaffected by dietary treatment. However, weekly growth was significantly lower with diets deprived of fish oil and containing lower levels of fish meal (0 and 4%) compared to higher levels (8 and 12%). Shrimp BW was significantly affected by the dietary inclusion of both fish oil and fish meal and their interaction, varying from 13.08 ± 0.72 (diet 0–0) to 14.82 ± 0.23 g (diet 2–12). Biofloc contained a high ash content (58.09 ± 3.01%), low lipid levels (1.67 ± 0.32%), and a 7.71–18.05% CP content. The isotopic signatures in shrimp muscle at harvest became more negative compared to values observed at stocking, approaching values of the diets used. We estimated that the experimental diets contributed on average with 91.5 ± 7.4% of the shrimp's carbon growth, with the remaining attributed to biofloc. Our results demonstrated that juvenile L. vannamei reared in a biofloc-dominated system derive the bulk of their nutrition and growth from artificial food. Biofloc acts as a supplemental food source, but provides a limited source of key dietary nutrients to shrimp growth.