Effects of chicken waste meal and vegetable substrate fed black soldier fly prepupae meal on rainbow trout (Oncorhynchus mykiss)

Abstract

A feeding trial was conducted to evaluate the effects of the dietary inclusion of black soldier fly (BSF), Hermetia illucens, prepupae in rainbow trout (Oncorhynchus mykiss) fingerling diets on growth performance, fillet quality, and gut and liver histology. Chicken waste meal and fruit & vegetable waste (1:9, v:v) were used as feeding substrates of BSF prepupae. Five diets were prepared: a basal diet (B0) based on fish meal (FM) and four additional diets in which BSF meal (BSFM) was used to replace 25, 50, 75, and 100% of the FM (B25, B50, B75, and B100, respectively). Orthogonal polynomial contrast was used to determine the trend between BSFM inclusion levels and growth parameters, fatty acids, and amino acids. Quadric relationships between the BSFM levels and growth parameters, including length and weight gain rate, specific growth rate (SGRW), and feed conversion rate, were determined. The optimum BSFM inclusion rate for the best SGRW was estimated at 11.9%. With the exception of the B100 group, increasing the BSFM level in the diet generally increases the fatty acid composition of whole fish. Dietary BSFM inclusion resulted in a significant increase in goblet cells in the proximal and distal intestines, as well as muscle layer thickness in the proximal intestine. A histological study showed that substituting fishmeal with BSFM had no effect on liver lipid accumulation. This study showed that replacing FM with BSFM in rainbow trout fingerling diets by 50% had no adverse effects on the growth performance, liver characteristics, feed utilisation, or fillet quality. Therefore, the BSFM described here can safely be used on rainbow trout fingerling diets. As a result, rainbow trout fingerlings can be fed 50% FM/BSFM replacement without adding additional essential amino acids to the diet or eliminating chitin from BSFM using the methods we used to culture BSF.