When a turbot catches a fly: Evaluation of a pre-pupae meal of the Black Soldier Fly (Hermetia illucens) as fish meal substitute - Growth performance and chitin degradation in juvenile turbot (Psetta maxima)

Larvae of black soldier flies (Hermetia illucens) are commercially produced on agricultural waste streams and convert these into animal body protein and fat. A feeding trial was carried out for 56 days in a recirculating aquaculture system (RAS) by replacing fish meal protein subsequently by Hermetia meal (HM) protein. Six diets were formulated for the replacement and contained 0%, 17%, 33%, 49%, 64%, and 76% of HM (54.1 +/- 1.1% crude protein, 13.4 +/- 0.7% crude lipid, dry matter basis). The diets were fed to triplicate groups of turbot 54.9 +/- 0.9 g once a day by hand until apparent satiation. Feed intake was affected by dietary HM inclusion and decreased with increasing HM incorporation due to low palatability. Growth performance was high, but affected by dietary HM inclusion. SGR was lower in all treatments containing HM whereas FCR was significantly higher at HM inclusion levels > 33%. Protein retention was highest at HM inclusion <= 33% and decreased significantly with increasing HM supplementation. Whole-body protein content was not affected by treatment, while body lipid decreased with increasing HM inclusion levels. The apparent digestibility coefficients (ADC) of HM were low for organic matter, crude protein, crude lipid, and gross energy. Chitinase activity or chitinolytic active bacteria were not detected in the mid gut of turbot. The presence of chitin might have influenced the feed intake, availability, and digestibility of the nutrients and therefore growth performance. In general, our study shows that the incorporation of HM protein in fish diets is possible, but limited by its low nutritive value. Considering that HM is produced on local greenhouse waste streams, HM might be a feasible alternative protein source for the partial replacement of fish meal. Further research on HM meal processing to increase nutrient utilization is needed. (C) 2012 Elsevier B.V. All rights reserved.