Evaluating the inclusion of Clostridium autoethanogenum protein instead of fishmeal protein in diets for European seabass (Dicentrarchus labrax): Growth performance, digestive enzymes, health status, and tissues investigations

The Clostridium autoethanogenum-derived protein (CAP) is a microbial protein generated during ethanol fermentation of agricultural byproducts. The present investigation evaluated the use of CAP as a sustainable alternative to reduce fishmeal (FM) dependency in aqua-feeds. A 70-day feeding trial was done to examine the impacts of partially replacing FM protein by CAP at 0 % (control, CAP0), 10 % (CAP10), 20 % (CAP20), 30 % (CAP30), and 50 % (CAP50) inclusion levels in diets for European seabass (Dicentrarchus labrax) juvenile (initial weight 10.5 ± 1.5 g). Results obtained demonstrated that dietary CAP incorporation up to 50 % FM replacement did not significantly (P > 0.05) impact the growth performance, feed efficiency, or survival rates. Similarly, the expression levels of growth-related genes (IGF-1 and GH) remained unchanged across treatments. The intestinal digestive enzymes activities, including lipase, alpha-amylase, and proteases, as well as the haematological parameters remained unaffected by the dietary CAP inclusion levels. Histological assessment revealed normal tissue architecture in the intestine, liver, and spleen of fish fed on CAP-containing diets. That indicats no adverse effects of CAP on organs’ structure. A simple economic analysis showed reduced feed costs with increasing CAP inclusion, where production costs per ton of fish gain decreases by 19.3 % at 50 % FM replacement compared to the control diet. These findings establish that CAP is a viable and cost-effective protein source capable of replacing up to 50 % FM protein in practical diets for D. labrax juveniles without compromising their growth, health status, or organs’ structure.