Effect of the inclusion of microalgae on the physical properties of extruded feed for gilthead seabream (Sparus aurata L.)

The inclusion of new ingredients in fish feed can affect the physical quality of the pellets. In order to study the effect of the addition of microalgae on the physical properties of the pellets, 15 extruded diets were studied that included three different species of microalgae (Nannochloropsis gaditana, Tetraselmis chuii and Chlorella vulgaris) at five different inclusion levels (0, 2.5, 5, 10 and 15%). The feed mixtures were extruded using a single-screw extruder (barrel temperature profile: 90–95–100 °C; die temperature: 105 °C; screw speed: 40–50 rpm). The physical properties studied included: expansion ratio, density, hardness, pellet durability index, water absorption index, water solubility index, floatability, sinking velocity, fat leakage and starch gelatinization. The present study showed that the physical properties of the pellets are influenced by the type and amount of microalgae used. The physical quality of the feed was modified, generally increasing its hardness and durability and reducing the fat leakage. •Microalgae are an interesting source of nutritional compounds for fish feed.•Microalgae were used at different inclusion levels to prepare pellets by extrusion.•The species of microalga and inclusion level affect the pellet's physical properties.•Microalgae improve the physical resistance of the pellets and reduce fat leakage.