The Replacement of Fish Meal with Poultry By-Product Meal and Insect Exuviae: Effects on Growth Performance, Gut Health and Microbiota of the European Seabass, Dicentrarchus labrax

Abstract

This study addressed the urgent need for sustainable protein sources in aquaculture due to the depletion of marine resources and rising costs. Animal protein sources, particularly poultry by-product meal (PBM) and insect exuviae meal, were investigated as viable alternatives to fishmeal (FM). The research study confirmed the successful replacement of FM with a combination of PBM and insect exuviae meal (up to 50%) in the diet of European seabass without compromising growth, feed conversion, gut health, and liver fat content. In particular, growth was robust with both PBM formulations, with the 25% PBM diet showing better results. Histological examinations showed good gut and liver health, contradicting the concerns of previous studies. This paper emphasizes the importance of holistic analyzes that go beyond growth parameters and include histomorphological investigations. The results show that PBM in combination with insect/exuviae meal is well tolerated by seabass, which is consistent with reports in the literature of it mitigating negative effects on gut health. A detailed analysis of the microbiota revealed a decrease in the Firmicutes/Proteobacteria ratio due to an increase in potentially pathogenic bacteria. However, the formulation containing insect exuviae partially counteracted this effect by preserving the beneficial Lactobacillus and promoting the synthesis of short-chain fatty acids (SCFAs), particularly butyrate. Chitin-rich components from insect exuviae were associated with improved gut health, which was supported by the increased production of SCFAs, which are known for their anti-inflammatory properties. This paper concludes that a combination of PBM and insect/exuviae meal can replace up to 50% of FM in the diet of seabass, supporting sustainable aquaculture practices. Despite some changes in the microbiota, the negative effects are mitigated by the addition of insect exuviae, highlighting their potential as a prebiotic to increase fish productivity and contribute to a circular economy in aquaculture.

Keywords: exuviae; gut microbiota; insect meal; poultry meal; seabass.

Figure 1

Standard hematoxylin-eosin (H&E) histochemical analysis of proximal (panels (A,C,E)) and distal (panels (B,D,F)) seabass intestine. We obtained 5 µm cross-sections from the proximal and distal paraffin-embedded intestine of CTRL (panels (A,B)), PM20 (panels (C,D)), and PM25 (panels (E,F)) fish. M, mucosa; SM, submucosa; CM, circular muscle layer; LM, longitudinal muscle layer. Scale bar = 1000 µm.

Figure 2

Standard haematoxylin–eosin (H&E) histochemical analysis of liver from representative images of fish fed control, PM20, and PM25 diets. We obtained 5 µm cross-sections from the paraffin-embedded liver of CTRL (panels (A,B)), PM20 (panels (C,D)), and PM25 (panels (E,F)) fish. Scale bar = 100 µm.

Figure 3

Stacked bar chart of the mean relative abundances (%) of the most abundant classified bacterial phyla (A) and families (B) most frequently found in feed samples.

Figure 4

Stacked bar chart of the mean relative abundances (%) of the most abundant classified bacterial phyla (A) and families (B) found in gut samples.

Figure 5

Plot of principal coordinate analysis (PCoA) using weighted (A) and unweighted (B) UniFrac distance matrices of gut microbial communities at the genus level.

Figure 6

Comparison of the relative abundance of the PICRUSt functional profile of the gut microbiota between the control and PM20 experimental groups. Only the predicted functional pathways that differ significantly (p < 0.05) are shown.

Figure 7

Comparison of the relative abundance of the PICRUSt functional profile of the gut microbiota between the control and PM25 experimental groups. Only the predicted functional pathways that differ significantly (p < 0.05) are shown.