The possibility of improving the physical quality of extruded fish feed using transglutaminase (TGase) treatment at different stages of the production process was investigated. The addition of TGase to the raw material mix and processing under high and medium moisture conditions significantly increased (p > 0.05) the durability, hardness and elasticity of fish feed pellets. However, the water stability of feeds was only improved when the TGase was applied in the vacuum coater; when it was mixed with the dry raw materials, the water stability of the product decreased. By further optimization of the enzyme dose when added to the vacuum coater, an increase in pellet durability was observed at enzyme dosages between 2.5 and 5 g kg(-1). Application of TGase in the coating step allowed an 87.5 % decrease in the dose of enzyme in feed produced under high moisture conditions. TGase treatment improves the physical quality of extruded fish feed, and the importance of optimization of enzyme dosage and processing conditions was demonstrated.