Microbial floc meal as a replacement ingredient for fish meal and soybean protein in shrimp feed

Abstract

Microbial flocs produced in suspended growth bioreactors could offer the shrimp industry a novel alternative feed. In this study, microbial flocs were produced in sequencing batch reactors (SBRs) using tilapia effluent and sugar as a growth media. It was determined that 1 kg of microbial floc could be produced per 1.49 kg of sucrose. These microbial flocs were tested as an ingredient for shrimp feed over a 35 day feeding trial. Two control diets (absent of microbial flocs) were compared against three dietary treatments (microbial floc inclusion). Control 1 and microbial floc diets (diets 1–3) were formulated to be equivalent for levels of crude protein, total fat, crude fiber, calcium, magnesium, phosphorus, potassium, and sodium. Controls 1 and 2 did not contain microbial flocs and differed slightly from each other in soybean oil, krill meal, and mineral/salt levels. For diet 1 (microbial floc 7.8%) and diet 2 (microbial floc 15.6%), soybean protein isolate on a protein basis was replaced with microbial flocs at a 7.8 and 15.6% inclusion level on a dry matter basis. For diet 3, fishmeal was replaced with microbial flocs at 7.8% and fish oil at 0.50% (microbial floc 7.8% + fish oil). Four juvenile Litopenaeus vannamei were stocked per tank and each dietary treatment was tested in 12 replicates over a 35 day feeding trial. No differences were observed between final survival rates (93 to 100%) between any of the dietary treatments. Growth (weight gain per week) for control 1, control 2, diet 1, diet 2, and diet 3 were respectively 1.09 ± 0.14, 0.88 ± 0.14, 1.64 ± 0.03, 1.61 ± 0.03, 1.63 ± 0.04 g/week. The total gain in weight for the three diets containing microbial floc of 8.07 to 8.18 g in five weeks with an initial weight of 0.44 ± 0.005 g is truly exceptional. Tukey's HSD (Honestly Significant Differences) test revealed that each of the three microbial floc diets significantly ( P < 0.01) outperformed each control in terms of weight gain per week with no differences in survival.