Ragaa, Naela M., et al. “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, vol. 16, no. 3, Feb. 2017, pp. 148–154, https://doi.org/10.3923/pjn.2017.148.154.