Impact of protein source properties and extrudate characteristics on feed intake and digestion in Spotted seabass (Lateolabrax maculatus)

Due to the diversification and variability of ingredients used in aquafeed formulas, producing extruded pellets with a targeted physical pellet quality (PPQ) is difficult and often unpredictable. Most research on PPQ in relation to changes in feed formulas, only made a comparison between ingredients (fishmeal vs alternative ingredients). Studies that considered the role of the physicochemical properties of the (alternative) ingredients on the final PPQ are rare. And there is still a lack of systematic research on the relationship among ingredient physicochemical properties, process conditions and pellet physical quality. Therefore, this project first aims to systematically assess the connection between ingredient physicochemical property, extrusion process conditions and PPQ. This is done by a (review) meta-analysis in which ingredient physicochemical properties and extrusion process conditions are related to PPQ parameters. PPQ has mainly been studied regarding aspects prior to consumption by fish. There is limited information on if and how PPQ affects pellet disintegration in the stomach of fish and thereby on gastric evacuation, digestive kinetics as well as on feed intake of fish. It is hypothesized that the impact of PPQ on digestive physiological responses in fish is dependent on the water salinity. This project also aims to study effects of extruded PPQ characteristics and environmental salinity on pellet disintegration in the stomach, gastrointestinal evacuation, feed intake regulation and nutrients digestion of fish. Via extrusion experiments, different batches of pellets with contrasting PPQ will be produced. These different batches of pellets are assessed in an in vitro test mimicking the disintegration of pellets in the stomach. Based on these results, a selected amount of batches will be tested in in vivo experiments regarding stomach evacuation, kinetics of digestion and feed intake in spotted seabass. In the last in vivo experiment, the interaction between PPQ and water salinity will be assessed.