Batch-to batch variation in nutrient digestbility of black soldier fly larvae meals in rainbow trout

The aim of this study was to evaluate the apparent digestibility coefficients (ADCs) of four batches of black soldier fly (BSF) meal, named BSF1, BSF2, BSF3 and BSF3, produced by the same company over one year, in rainbow trout (Oncorhynchus mykiss). To assess nutrients and amino acids ADCs, each insect meal was mixed with a high-quality reference diet in a 30:70 ratio on as is basis, including celite as inert marker, and pelleted. The reference diet was also used as control. The ADCs were calculated based on the data collected and determined during an in vivo experiment. A total of 240 fish were randomly divided into 250-L cylindroconical tanks supplied in flow-through open and Choubert systems (3 replicates/treatment). Data were analysed by One-Way ANOVA (SPSS V20.0.0.; P ≤ 0.05). Globally, the four BSF meals showed a high ADC value, between 82.6 and 100%. No statistically significant differences were observed in the ADCs of dry matter, crude protein, ether extract and gross energy, while some differences were observed in the amino acid profile (P < 0.05). Generally, fish fed on BSF1 displayed reduced digestibility for histidine, isoleucine, leucine, valine, alanine, proline, and glycine compared to BSF2 and BSF4 meals (P < 0.05), while the BSF3 group showed intermediate results (P > 0.05). Despite the good digestibility of nutrients for all the insect mealsthe implementation of standardized production is important to have a standardize BSF meal capable of meeting market demands.