Since insect meals have begun to take center stage as next generation feed ingredients , there has been a pressing need to validate its effects on popular species such as Atlantic salmon (Salmo salar ). Currently, t here are only a few published trials evaluating the inclusion of black soldier fly larvae meal (Hermetia illucens) to replace fish meal in the diet of salmonids, yet the substitution of soy protein concentrate (SPC) and the use of full-fat yellow mealworm (Tenebrio molitor) remains novel. Thus, the aim of this trial was to evaluate the impact these two insect meals have on the growth performance and nutrient utilization of post-smolt Atlantic salmon.
Material & Methods
An 11- week trial was conducted at the Mørkvedbukta R esearch S tation, Nord University (Bodø, Norway) under a continuous light regime (24L: 0D) with 520 fish with an average initial weight of 143.05 ± 12.89 g divided into 4 replicates of 26 fish per diet group randomly assigned to one of 20 tanks (870 cm3 ) in a saltwater flow-through system equipped with feed collectors. The experimental diets consisted of a control (CTRL) diet based on 20% FM, 14.46% wheat gluten, and 20% SPC as primary protein sources, two diets substituting wheat gluten and SPC with 5 and 10% full-fat black soldier fly larvae meal (BSF5 and BSF10), and two diets containing 15 and 30% full-fat mealworm (MW15 and MW30), respectively. FM inclusion of 20% was maintained constant in all formulations. Fish were fed by automatic feeders at a rate of 1.6% body weight. Uneaten feeds were collected twice daily. Biometric data of all fish was recorded prior to and at the end of the experiment. In addition, samples for chemical composition (whole fish and feces) were collected to study digestibility and nutrient retention.
Results based on data collected at the end of the trial indicated that the inclusion of insect meal in the diet of post-smolt Atlantic salmon had no significant effects on growth performance or organo somatic indices (weight gain, condition factor, feed conversion ratio, specific growth rate, hepatosomatic index and viscerosomatic index). All groups underwent a roughly three-fold increase in weight with no mortality during the experimental period. Additionally, there were no significant differences observed in macronutrient retention with an average percent amongst the groups of 60.5, 58.3, and 47.8% for lipid, protein, and energy, respectively. Lastly, no significant differences were observed in the apparent digestibility coefficients (ADCs) of dry matter (DM), ash, or energy. However, protein digestibility in the MW30 diet (80.4%) was significantly lower (P ≤ 0.05) compared to the CTRL diet (84.5%). The ADC of lipid will be available at the time of the conference.
The growth performance data revealed no significant differences between the dietary treatment groups , with weight gain following a similar trend as that of other trials that investigated the replacement of FM with BSF meal, and the absence of mortality during the trial period . Our growth results are in agreement with previous studies on inclusion of BSF meal; in Atlantic salmon diets up to 12.5% and up to 15% , and in rainbow trout (Onchorhynchus mykiss ) diets up to 18%. Similarly, inclusion of MW meal at 18% in rainbow trout diet did not negatively affect growth. As observed in our study, previous studies by Weththasinghe et al., and Fawole et al., have also reported that insect meal inclusion does not infl uence protein and lipid retention, respectively in Atlantic salmon. Lastly, results of protein ADC in the experimental diets showed significantly lower digestibility in the MW30 diet compared to the control . There are few studies for comparison which utilized meal worm in salmonid feeds . The closest trial by Rema et al., found that up to 100% (25% FM) could be replaced without any effect on protein digestibility. However, our trial differs in that it replaces non FM protein sources with full-fat insect meal rather than defatted meal.
The overall results of this study show that the inclusion of either BSF meal or MW meal in the diet of Atlantic salmon does not have any significant negative effects on growth performance, nutrient retention . However, there were differences in protein ADC with 30% inclusion of mealworm. This demonstrates that insect meals can be used as an alternative to, not only fish meal, as has been validated in previous studies, but also to plant derived sources as well . These results contribute to the growing body of knowledge on insect meal inclusion and thus the increased diversification of aquafeed ingredients for greater sustainability in the aquaculture sector .
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