Complementarity of insect meal and poultry by-product meal as replacement for fishmeal can sustain the production performance of European perch (Perca fluviatilis), reduce economic fish-in fish-out ratio and food-feed competition, and influence the environmental indices

Defatted black soldier fly (Hermetia illucens) (DHI) and poultry by-product meal (PBM) were used in tandem to substitute fishmeal in diets for European perch (Perca fluviatilis) in the current study. Four isoproteic (52%), isolipidic (14%), and isoenergetic (22 Mj/kg) diets (abbreviated diets: COM0, COM50, COM75, and COM100) were formulated, in which DHI replaced 0, 50, 75 and 100% fishmeal with the complementarity of PBM, and fed to triplicate groups of European perch (54.43 ± 0.35 g) for 90 days.
Dietary treatments had no effect on growth performance indices of final body weight (P = 0.209) and survival (P = 0.155), feed utilization as illustrated by daily feed intake (P = 0.595), feed conversion ratio (P = 0.073), and condition factor (P = 0.209). On the other hand, specific growth rate and weight gain were significantly affected by treatments (P = 0.011 and 0.012, respectively) and were DHI level-dependent (P = 0.006 and 0.010, respectively). Protein digestibility was statistically greater in COM75 and COM50 than in COM100 (P < 0.001). Ash digestibility was DHI-inclusion dependent (P = 0.001). Dietary complementarity significantly impacted the colour (P < 0.05), dripping loss (P = 0.008), moisture (P = 0.022), and docosahexaenoic acid (P < 0.001) of perch fillets.
DHI-PBM substitution of 75% fishmeal did not significantly increase nitrogen waste (P > 0.05), but did at 100% replacement (P = 0.03). In contrast, the diet treatments sustained total solid and phosphorus waste relative to the control group (P = 0.18 and 0.107, respectively). Dietary complementary, on the other hand, resulted in a greater impact on global warming potential (P = 0.019) and water use (P < 0.001), but did not affect land use (P = 0.55).
The use of DHI and PBM in diets for European perch offered great benefit concerning less reliance of aquaculture on forage fish from marine sources as illustrated by the economic Fish-in Fish-out ratio, which significantly decreased with increasing level of complementarity (P < 0.0001), and reduced food-feed competition.
The results from the present study revealed that the combination of DHI and PBM can replace fishmeal at as high as 50% while favoring all metrics relative to the control group.