Aquaculture Reports (Nov 2021)
Physical feed quality and starch content causes a biological response in Atlantic salmon (Salmo salar L)
Abstract
The aim of this study was to investigate the effect of starch content and pellet physical quality on the biological response in Atlantic salmon. Salmon feeds with a large variation in physical quality were produced by the adjustment of dietary starch inclusion (92 g kg−1 or 64 g kg−1), preconditioner oil (0.0 or 11.0 kg h−1), extruder moisture addition (13.5 or 27 kg h−1) and drying temperature (38 °C or 70 °C). The variables impacted physical quality for the 12 feed codes and with hardness S (standing) and Durability measured in the range of 39–212 N and 39–94 %, respectively. Gently dried feed (38 °C) was harder and more durable than conventionally dried (70 °C). This could be explained by the phase transition theory and drying in the mobile rubbery phase above the glass transition temperature (Tg) for the gently dried feed codes. All feed codes were evaluated in Atlantic salmon performance and digestibility trials. There was a significant difference between the codes for weight gain (%; P < 0.001), specific and thermal growth rate (P < 0.01) and protein efficiency ratio (P < 0.01). Growth was negatively associated with increased starch content, hardness and durability parameters and reduced solubility, fat content and gross energy. The most important physical properties affecting growth performance were Hardness S, Durability and Doris dust, parameters that may represent feed hydration- and dissolution rates. This study documents that the impact of pellet physical quality should be considered when evaluating the results from biological fish trials.
