The need to diversify novel feed ingredients for aquaculture is becoming increasingly important. Black soldier fly larvae (BSFL, Hermetia illucens) meal is gaining much interest due to its unparalleled efficiency at converting a wide variety of substrates into usable protein and fats. Such attributes could increase product circularity and sustainability in agreement with the Sustainable Development Goals (SDGs). To date, few studies have investigated the use and effects of the inclusion of BSFL meal in either terrestrial or aquatic farmed animal diets. This study assessed the behaviour of salmon fry (Salmo salar) fed on three different diets – Control diet (CD, commercial diet), de-chitinised insect meal at 2.5% inclusion (BSFL-D2.5), and de-chitinised insect meal at 25.0% inclusion (BSFL-D25). Diets were fed to naïve first feeding fry for 21 days. Growth and diet consumption was monitored every day and behaviour was recorded and analysed at the end of the trial to explore potential differences in feeding related behaviours.
An ethogram (a full suite of behaviours exhibited by fish in each treatment group) was constructed for the purpose of the study and four feeding related behaviours were selected: darting, zone-crossing, upper zone positioning and aggression. Fish were observed displaying different behaviours depending on the diet treatments (Figure 1a). Significantly more darting and zone-crossing behaviours were observed between the BSFL-D2.5 and CD group which maintained positions near the water surface to feed (Figure 1b). A similar final average weight between these two groups suggested that despite the adoption of different feeding strategies neither growth or condition was affected. Interestingly, higher darting in the BSFL-D2.5 reflected a more natural feeding strategy which may improve welfare, in addition higher overall activity may improve flesh quality in the long term. The BSFL-D25 diet displayed lower levels of feeding behaviour which translated to a lower final average weight. There were no significant differences in the levels of aggressive behaviour between the insect-meal diets and the CD groups indicating that no negative effects arise from the use of BSFL diets. Further research is required to determine whether insect-based feeds indeed elicit natural feeding behaviour in juvenile salmon and the implications on the welfare of the species.