In recent years, the aquafeed industry has witnessed the introduction of several new ingredients derived from food by-product upcycling, particularly from Single-Cell Protein (SCP). SCP are bulks of dried cells , produced by algae, yeast, bacteria and fungi, that have been progressively tested as protein rich supplements or ingredients in aquafeed. Bacteria meals are especially promising ingredients but their digestibilities have only been estimated in salmonids and data is missing for tropical fish species.
This study gathers the learning of three trials conducted on 2700 (48.2g) and 225 (48.9g) Asian seabass (Lates calcarifer) and 225 (48.7g) saline tilapia (Oreochromis mossambicus ). Fish fed with experimental diets containing 30% of various bacteria meals and d iets were produced either with a twin-screw extruder or a screw-press, and 0.1% Yttrium oxide was added to estimate digestibility. In small and large fish trials, thermal-unit growth coefficient (TGC), feed conversion rate (FCR) and nutrient retention efficiency were measured. Fish faeces were collected in each tank, diet and ingredient digestibility were estimated for protein, energy, and amino acids. The impact of extrusion parameters on gut enzyme activity and gut transcriptomics analysis was also explored. In saline tilapia, the bacteria meal ADC’s for were 62.8±13.3% for dry matter and 77.6±4.1% for protein. In barramundi, the bacteria meal ADCs were 70.1±1.0 for dry matter and 79.1±0.7% for protein. Finally, the strategy for optimizing extrusion parameters is discussed to improve SCP digestibility.