Aquaculture is the fastest-growing food-producing sector in the world, and for this industry to continue expanding, there must be improved sustainability. One of the ways to achieve this goal is to use higher amounts of terrestrially based ingredients. Traditionally this has relied on using plant-based proteins and lipids, however, there is increasing interest in the use of insect meals. Recently, interest arose to evaluate a byproduct of the insect industry (EnviroFlight, LLC.) called “frass”. It is composed of spent feed and waste products from the black soldier fly (Hermetia illucens) larvae and contains 38% carbohydrate and 22% crude protein. Thus, it could be new ingredient for fish. The aim of this study was to evaluate the nutritional potential of frass in Nile tilapia (Oreochromis niloticus).
Six diets (isonitrogenous: 300 g/kg crude protein and isoenergetic: 4300 kcal/kg) were formulated to trade the carbohydrate, lipid and protein nutrients with increasing levels of frass to replace the blend of plant ingredients that included soybean meal, corn-DDGS and wheat flour. Diets were as follows: Diet 1: Control (fish meal: 8%, corn DDGS: 30%, SBM: 33% and wheat flour: 23%); and Diets 2 – 6: 10, 20, 30, 40 and 50% frass was used to replace the blend of plant ingredients in the diets. Nile tilapia fingerlings (ave. weight: 2.0 g) were randomly distributed in 18 tanks (25 L, each tank contains 20 fish) in a recirculatory aquaculture system. Fish were fed 3 times per day at satiation level for nine weeks.
At the end of the trial, the weight gain (%) was higher in diet 6 (50% frass) than other groups (Fig.1), however, feed utilization showed no differences (P<0.05). The gluconeogenic gene mRNA expression indicates that the fish fed 30% frass had the lowest expression of glucose-6-phosphatase-2 (G6pca2) gene compared to other groups, but no significant variation was noticed in the G6pca1. The histological evaluation indicates that the fish fed the frass-based diets showed some hepatic inflammation and vacuolization (Fig.2). Conclusively, highest growth performance was observed at 50% inclusion of frass in the tilapia diet, however, it does appear that the nutritive value of frass could be further improved based on the observed hepatic alteration. Nevertheless, this frass product replaced 33, 54 and 64% of the protein, lipid and carbohydrate fraction in Nile tilapia diet, respectively, and could be an additional ingredient in tilapia diets to improve aquaculture sustainability.