Ragaa, Naela M., Nermeen M. Abu Elala, Azza M. Kamal, and N.F. Kamel. 2017. “Effect of a Serine-Protease on Performance Parameters and Protein Digestibility of Cultured Oreochromis Niloticus Fed Diets With Different Protein Levels”. Pakistan Journal of Nutrition 16 (3): 148–154. https://doi.org/10.3923/pjn.2017.148.154.