Introduction
Over the past decade, aquaculture and particularly Atlantic salmon farming have undergone a significant nutritional transition, shifting from a fishmeal-based diet to relying on plant-based ingredients1. While this shift has contributed to reduced dependency on marine resources, it has also raised concerns relating to land use, health, gut function, and fillet quality2,3. Additionally, the volatility in prices and availability of both marine and land-based raw materials is intensifying the search for novel, sustainable, and functional feed ingredients. Insect meal has emerged as a promising candidate, considered a well-suited nutrient source for salmonids, which naturally consume insects in their riverine habitats4. The objective of the study was to determine whether 50% of fish meal content in freshwater phase Atlantic salmon diets could be replaced with partially defatted Black Soldier Fly Larvae (BSFL) meal (corresponding to 10% inclusion of BSFL meal in the diet), and its impact on key performance indicators such as growth performance and feed efficiency.
Materials and Methods
Defatted Black Soldier Fly Larvae (BSFL) meal from Innovafeed replaced 50% of fishmeal in the test diet (corresponding to a 10% inclusion), which was otherwise iso-proteic and iso-energetic to a fishmeal/SPC control. 100 juvenile Atlantic salmon (17.5g initial weight) per tank (n=4 replicates/diet) were fed to satiation 4 times daily for 8 weeks. Feed intake, g rowth (initial and final weight, SGR, FCR), mortality, and VSI (5 fish/tank at termination) were measured. All parameters were assessed for normality and homogeneity of variance prior to statistical analysis. Subsequently, comparisons were performed using a Student’s t-test.
Results
After eight weeks of study, the highest feed intake was observed in the insect-meal fed group (+ 4%, p > 0.05), which also had a higher final weight (+ 5%, p < 0.05) compared to fish fed the fishmeal based control. This higher final weight translated into a significantly higher specific growth rate (SGR) for the diet with 10% insect meal (1.44 vs. 1.35, p = 0.0136). Interestingly, despite a higher feed intake, there was a trend for the feed conversion ratio (FCR) of the test feed to be better than the control feed (0.91 vs. 0.96, p = 0.0716 ). Regarding fish mortality, physiologic state and health , no differences were measured between the control and test groups. More specifically, mortality was below 1% in both groups, and viscero somatic index (VSI) was similar in the control and test groups (14.7 for the control diet and 14.9 for the test diet, with no statistical significance).
Discussion
The results obtained were particularly interesting in regards to previous studies. The improved growth performance (higher SGR, trend for better FCR) observed in our freshwater salmon trial with a 10% inclusion rate, corresponding to 50% replacement of fishmeal by insect meal offers a contrast to other studies such as Belgit et al.’s, which reported no significant effects at a 60% BSFL inclusion replacing both fishmeal and SPC5 . As highlighted by Weththasinghe et al.’s meta-analysis, the BSFL inclusion rate and the type and percentage of protein replaced are critical6. Additionally, the absence of visceral fat accumulation in our study, unlike at higher inclusion rates (Belgit et al.5), further underscores the importance of the inclusion level.
Conclusion
These findings indicate that a moderate level of insect meal inclusion can effectively enhance growth and feed utilization in juvenile Atlantic salmon reared in freshwater. This overperformance should be considered in the economic evaluation of incorporating insect meal as a sustainable and performance-enhancing ingredient in salmonid aquaculture.
References:
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2. Francis, G., Makkar, H. P. S. & Becker, K. Antinutritional factors present in plant-derived alternate fish feed ingredients and their effects in fish. Aquaculture 199, 197–227 (2001).
3. Boissy, J. et al. Environmental impacts of plant-based salmonid diets at feed and farm scales. Aquaculture 321, 61–70 (2011).
4. FAO: Natural food and feeding habits. https://www.fao.org/fishery/affris/species-profiles/atlantic-salmon/natural-food-and-feeding-habits/en/.
5. Belghit, I. et al. Potential of insect-based diets for Atlantic salmon (Salmo salar ). Aquaculture 491, 72–81 (2018).
6. Weththasinghe, P., Hansen, J. Ø., Mydland, L. T. & Øverland, M. A systematic meta-analysis based review on black soldier fly (Hermetia illucens ) as a novel protein source for salmonids. Reviews in Aquaculture 14, 938–956 (2022).